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109-513: Distillation , also classical distillation , is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still . Dry distillation ( thermolysis and pyrolysis ) is the heating of solid materials to produce gases that condense either into fluid products or into solid products. The term dry distillation includes

218-421: A theoretical plate ) will yield a purer solution of the more volatile component. In reality, each cycle at a given temperature does not occur at exactly the same position in the fractionating column; theoretical plate is thus a concept rather than an accurate description. More theoretical plates lead to better separations. A spinning band distillation system uses a spinning band of Teflon or metal to force

327-460: A Chinese Buddhist pilgrim who visited the city via the Silk Road , had given its name's meaning as "cut-off head". With the help of a Jataka , he had interpreted it to be the place where Gautama Buddha —during a previous birth as Pusa or Chandaprabha —cut off his head to feed a hungry lion. This tradition still persists with the area in front of Sirkap (also meaning "cut-off head"), which

436-561: A World Heritage Site . By some accounts, the University of ancient Taxila is considered to be one of the earliest universities or education centre in South Asia. Other scholars do not consider it to have been a university in the modern sense, in that the teachers living there may not have had official membership of particular colleges, and there did not seem to have existed purpose-built lecture halls and residential quarters in

545-431: A chemical plant . Some types of separation require complete purification of a certain component. An example is the production of aluminum metal from bauxite ore through electrolysis refining . In contrast, an incomplete separation process may specify an output to consist of a mixture instead of a single pure component. A good example of an incomplete separation technique is oil refining. Crude oil occurs naturally as

654-405: A batch distillation setup (such as in an apparatus depicted in the opening figure) until the mixture is boiling results in a vapor above the liquid that contains a mixture of A and B. The ratio between A and B in the vapor will be different from the ratio in the liquid. The ratio in the liquid will be determined by how the original mixture was prepared, while the ratio in the vapor will be enriched in

763-796: A battle since the city was immediately surrendered to the Macedonian Empire . This was followed successively by the Maurya Empire (~317 - ~200 BCE), the Indo-Greek Kingdom (~200 BCE - ~55 BCE), the Indo-Scythians (~80 BCE - ~30 CE), and the Kushan Empire (~ 30 CE - ~375 CE), who destroyed the existing city, in the first century CE, to build their own on a site to the north of the ruins. Owing to its strategic location, Taxila has changed hands many times over

872-526: A blow from which the city would never recover. From 500 CE to 540 CE, the city languished after falling under the control of the Hunnic Empire ruled by Mihirakula . Mihirakula presided over some destruction of Buddhist sites, monasteries and Hindu temples across northwestern regions of the Indian subcontinent. Xuanzang visited India between 629 and 645 CE. Taxila which was desolate and half-ruined

981-439: A boiling point, although this is because its composition changes: each intermediate mixture has its own, singular boiling point. The idealized model is accurate in the case of chemically similar liquids, such as benzene and toluene . In other cases, severe deviations from Raoult's law and Dalton's law are observed, most famously in the mixture of ethanol and water. These compounds, when heated together, form an azeotrope , which

1090-671: A clear technological change from the Period I material. Seven radiocarbon dates were also taken from the earlier and later Period II/Kot Diji, and seem to show this phase dates from the mid-late 3rd to early 2nd millennium BCE. Gandhara was an ancient Indo-Aryan kingdom of western South Asia whose existence was attested during the Iron Age . The capital of the kingdom was in Taxila. The first major settlement at Taxila, in Hathial mound,

1199-508: A distinctive type of highly burnished pottery that shows clear signs of the use of woven baskets in the manufacturing process and the application of a slurry to the exterior surface. Periods IA and II at Sarai Khola seem to show continuity from Period I, with the appearance of red burnished wares. However, Kot Diji -style wares were found in greater numbers, and the Kot Diji-style forms show signs of having been wheel-thrown, marking

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1308-690: A dough made of rye flour. These alembics often featured a cooling system around the beak, using cold water, for instance, which made the condensation of alcohol more efficient. These were called pot stills . Today, the retorts and pot stills have been largely supplanted by more efficient distillation methods in most industrial processes. However, the pot still is still widely used for the elaboration of some fine alcohols, such as cognac , Scotch whisky , Irish whiskey , tequila , rum , cachaça , and some vodkas . Pot stills made of various materials (wood, clay, stainless steel) are also used by bootleggers in various countries. Small pot stills are also sold for use in

1417-410: A few exceptions, elements or compounds exist in nature in an impure state. Often these raw materials must go through a separation before they can be put to productive use, making separation techniques essential for the modern industrial economy. The purpose of separation may be: Separations may be performed on a small scale, as in a laboratory for analytical purposes, or on a large scale, as in

1526-484: A great centre of learning with world-famous teachers. The Jatakas mention non-Buddhist institutions and teachers in Taxila. They show the predominance of Vedic and technical disciplines including law, medicine, and military science. The Takkasila Jataka, more commonly known as the Telapatta Jataka, tells the tale of a prince of Benares who is told that he would become the king of Takkasila if he could reach

1635-576: A group of proper settlements around 1000 BCE, it is a UNESCO World Heritage Site , being one of the oldest settlements in South Asia. It has a population of over 136,900, as of 2023 ; and is administratively located in the Taxila Tehsil of Rawalpindi District , lying approximately 25 kilometres (16 mi) northwest of the Islamabad–Rawalpindi metropolitan area and immediately south of Haripur District , Khyber Pakhtunkhwa . Old Taxila

1744-594: A gymnastic and equestrian contest there. On Alexander's death, in 323 BCE, the province and much of the once Achaemenid territories would pass to his general Seleucus I Nicator and founder of the successor Seleucid Empire . By 303 BCE, the Seleucid Empire's satraps in South Asia had been formally annexed by the expanding Mauryan empire, following the Seleucid–Mauryan war , with the provincial capital and center of higher education at of Taxila now under

1853-408: A lower concentration in the vapor. Indeed, batch distillation and fractionation succeed by varying the composition of the mixture. In batch distillation, the batch vaporizes, which changes its composition; in fractionation, liquid higher in the fractionation column contains more lights and boils at lower temperatures. Therefore, starting from a given mixture, it appears to have a boiling range instead of

1962-888: A man". The Kidarites , vassals of the Hephthalite Empire are known to have invaded Taxila in c. 450 CE. Though repelled by the Gupta Emperor Skandagupta , the city would not recover- probably on account of the strong Hunnic presence in the area, breakdown of trade as well as the three-way war among Persia, the Kidarite State, and the Huns in Western Gandhara . The White Huns and Alchon Huns swept over Gandhāra and Punjab around 470 CE, causing widespread devastation and destruction of Taxila's famous Buddhist monasteries and stupas ,

2071-399: A mixture of various hydrocarbons and impurities. The refining process splits this mixture into other, more valuable mixtures such as natural gas , gasoline and chemical feedstocks , none of which are pure substances, but each of which must be separated from the raw crude. In both complete separation and incomplete separation, a series or cascade of separations may be necessary to obtain

2180-463: A movable liquid barrier. Finally, the entry of undesired air components can be prevented by pumping a low but steady flow of suitable inert gas, like nitrogen , into the apparatus. In simple distillation, the vapor is immediately channeled into a condenser. Consequently, the distillate is not pure but rather its composition is identical to the composition of the vapors at the given temperature and pressure. That concentration follows Raoult's law . As

2289-475: A number of monuments and other historical places of note in the area besides the four settlements at Bhir, Saraikala, Sirkap, and Sirsukh. They number 18 in all: In a 2010 report, Global Heritage Fund identified Taxila as one of 12 worldwide sites most "on the Verge" of irreparable loss and damage, citing insufficient management, development pressure, looting, and war and conflict as primary threats. In 2017, it

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2398-435: A pair of sandals, or an umbrella. In cases of poor students being unable to afford even that, they could approach the king, who would then step in and provide something. Not providing a poor student a means to supply his Guru's Dakshina was considered the greatest slur on a King's reputation. Examinations were treated as superfluous, and not considered part of the requirements to complete one's studies . The process of teaching

2507-441: A result, simple distillation is effective only when the liquid boiling points differ greatly (rule of thumb is 25 °C) or when separating liquids from non-volatile solids or oils. For these cases, the vapor pressures of the components are usually different enough that the distillate may be sufficiently pure for its intended purpose. A cutaway schematic of a simple distillation operation is shown at right. The starting liquid 15 in

2616-424: A vacuum pump. The components are connected by ground glass joints . For many cases, the boiling points of the components in the mixture will be sufficiently close that Raoult's law must be taken into consideration. Therefore, fractional distillation must be used to separate the components by repeated vaporization-condensation cycles within a packed fractionating column. This separation, by successive distillations,

2725-722: A water-cooled still, by which an alcohol purity of 90% could be obtained. The distillation of beverages began in the Southern Song (10th–13th century) and Jin (12th–13th century) dynasties, according to archaeological evidence. A still was found in an archaeological site in Qinglong, Hebei province, China, dating back to the 12th century. Distilled beverages were common during the Yuan dynasty (13th–14th century). In 1500, German alchemist Hieronymus Brunschwig published Liber de arte distillandi de simplicibus ( The Book of

2834-726: A wide column with a large holdup. Conversely, a column with a low reflux ratio must have a large number of stages, thus requiring a taller column. Both batch and continuous distillations can be improved by making use of a fractionating column on top of the distillation flask. The column improves separation by providing a larger surface area for the vapor and condensate to come into contact. This helps it remain at equilibrium for as long as possible. The column can even consist of small subsystems ('trays' or 'dishes') which all contain an enriched, boiling liquid mixture, all with their own vapor–liquid equilibrium. There are differences between laboratory-scale and industrial-scale fractionating columns, but

2943-495: Is a distillery of alcohol . These are some applications of the chemical separation process that is distillation: Early evidence of distillation was found on Akkadian tablets dated c.  1200 BCE describing perfumery operations. The tablets provided textual evidence that an early, primitive form of distillation was known to the Babylonians of ancient Mesopotamia . According to British chemist T. Fairley, neither

3052-416: Is a flow from the condenser back to the column, which generates a recycle that allows a better separation with a given number of trays. Equilibrium stages are ideal steps where compositions achieve vapor–liquid equilibrium, repeating the separation process and allowing better separation given a reflux ratio. A column with a high reflux ratio may have fewer stages, but it refluxes a large amount of liquid, giving

3161-453: Is also referred to as rectification. As the solution to be purified is heated, its vapors rise to the fractionating column . As it rises, it cools, condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors is determined once again by Raoult's law. Each vaporization-condensation cycle (called

3270-478: Is during this time that the city heavily features in classical Indian literature – both as a centre of culture as well as a militarised border city. Taxila's university remained in existence during the travels of Chinese pilgrim Faxian, who visited Taxila around 400 CE. He wrote that Taxila's name translated as "the Severed Head", and was the site of a story in the life of Buddha "where he gave his head to

3379-511: Is found in the Hathial section, which yielded pottery shards that date from as early as the late 2nd millennium BCE to the 6th century BCE. The Bhir Mound ruins at the site date from the 6th century BCE, and are adjacent to Hathial. The ruins of Sirkap date to the 2nd century BCE, and were built by the region's Greco-Bactrian kings who ruled in the region following Alexander the Great's invasion of

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3488-486: Is heated, the vapor pressure of each component will rise, thus causing the total vapor pressure to rise. When the total vapor pressure reaches the pressure surrounding the liquid, boiling occurs and liquid turns to gas throughout the bulk of the liquid. A mixture with a given composition has one boiling point at a given pressure when the components are mutually soluble. A mixture of constant composition does not have multiple boiling points. An implication of one boiling point

3597-403: Is identified with kingdom of Taxila by some authors. By some accounts, Taxila was considered to be one of the earliest (or the earliest) universities in the world. The school consisted of several monasteries without large dormitories or lecture halls where the religious instruction was provided on an individualistic basis. Others do not consider it a university in the modern sense, in that

3706-584: Is most famous for ruins of several settlements, the earliest dating from around 1000 BCE. It is also known for its collection of Buddhist religious monuments, including the Dharmarajika stupa , the Jaulian monastery, and the Mohra Muradu monastery. The main ruins of Taxila include four major cities, each belonging to a distinct time period, at three different sites. The earliest settlement at Taxila

3815-476: Is said to have been enthroned at Takshashila. The Ramayana describes Takshashila as a magnificent city famed for its wealth which was founded by Bharata, the younger brother of Rama . Bharata, who also founded nearby Pushkalavati , installed his two sons, Taksha and Pushkala, as the rulers of the two cities. In the Buddhist Jatakas, Taxila is described as the capital of the kingdom of Gandhara and

3924-414: Is that lighter components never cleanly "boil first". At boiling point, all volatile components boil, but for a component, its percentage in the vapor is the same as its percentage of the total vapor pressure. Lighter components have a higher partial pressure and, thus, are concentrated in the vapor, but heavier volatile components also have a (smaller) partial pressure and necessarily vaporize also, albeit at

4033-399: Is when the vapor phase and liquid phase contain the same composition. Although there are computational methods that can be used to estimate the behavior of a mixture of arbitrary components, the only way to obtain accurate vapor–liquid equilibrium data is by measurement. It is not possible to completely purify a mixture of components by distillation, as this would require each component in

4142-822: The Indian Ocean from the mouth of the Indus to the Suez . Darius then returned to Persia via the Bolan Pass . The region continued under Achaemenid suzerainty under the reign of Xerxes I, and continued under Achaemenid rule for over a century. Taxila was sometimes ruled as part of the Gandhara kingdom (whose capital was Pushkalavati), particularly after the Achaemenid period, but Taxila sometimes formed its own independent district or city-state. During his invasion of

4251-477: The Indus Valley , Alexander the Great was able to gain control of Taxila ( Ancient Greek : Τάξιλα ) in 326 BCE without a battle, as the city was surrendered by its ruler, king Omphis (Āmbhi). Greek historians accompanying Alexander described Taxila as "wealthy, prosperous, and well governed". Arrian writes that Alexander was welcomed by the citizens of the city, and he offered sacrifices and celebrated

4360-612: The Tirthankaras , visited Taxila millions of years ago. His footprints were subsequently consecrated by Bahubali who erected a throne and a dharmachakra ('wheel of the law') over them several miles in height and circumference. The region around Taxila was settled by the Neolithic era, with some ruins at Taxila dating to 1000 BCE. Ruins dating from the Early Harappan period around 1300 BCE have also been discovered in

4469-407: The vapor pressure of the liquid equals the pressure around the liquid, enabling bubbles to form without being crushed. A special case is the normal boiling point , where the vapor pressure of the liquid equals the ambient atmospheric pressure . It is a misconception that in a liquid mixture at a given pressure, each component boils at the boiling point corresponding to the given pressure, allowing

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4578-627: The 3rd century. Distillation was practiced in the ancient Indian subcontinent , which is evident from baked clay retorts and receivers found at Taxila , Shaikhan Dheri , and Charsadda in Pakistan and Rang Mahal in India dating to the early centuries of the Common Era . Frank Raymond Allchin says these terracotta distill tubes were "made to imitate bamboo". These " Gandhara stills" were only capable of producing very weak liquor , as there

4687-405: The 7th-century Buddhist monk. Unlike Pliny, these sources noted that the journey to Taxila from the Indus took three days and not two. Cunningham's subsequent explorations in 1863–64 of a site at Shah-dheri convinced him that his hypothesis was correct. Now as Hwen Thsang, on his return to China, was accompanied by laden elephants, his three days' journey from Takhshasila [ sic ] to

4796-617: The Apostle visited Gondophares IV around 46 CE, possibly at Taxila given that city was Gondophares' capital city. Around the year 50 CE, the Greek Neopythagorean philosopher Apollonius of Tyana allegedly visited Taxila, which was described by his biographer, Philostratus , writing some 200 years later, as a fortified city laid out on a symmetrical plan, similar in size to Nineveh . Modern archaeology confirms this description. Inscriptions dating to 76 CE demonstrate that

4905-612: The Art of Distillation out of Simple Ingredients ), the first book solely dedicated to the subject of distillation, followed in 1512 by a much expanded version. Right after that, in 1518, the oldest surviving distillery in Europe, The Green Tree Distillery , was founded. In 1651, John French published The Art of Distillation , the first major English compendium on the practice, but it has been claimed that much of it derives from Brunschwig's work. This includes diagrams with people in them showing

5014-545: The Greeks nor the Romans had any term for the modern concept of distillation. Words like "distill" would have referred to something else, in most cases a part of some process unrelated to what now is known as distillation. In the words of Fairley and German chemical engineer Norbert Kockmann respectively: The Latin "distillo," from de-stillo, from stilla, a drop, referred to the dropping of a liquid by human or artificial means, and

5123-436: The Indus at Utakhanda , or Ohind, must necessarily have been of the same length as those of modern days, and, consequently, the site of the city must be looked for somewhere in the neighbourhood of Kâla-ka-sarâi . This site is found near Shah-dheri , just one mile to the north-east of Kâla-ka-sarâi , in the extensive ruins of a fortified city, around which I was able to trace no less than 55 stupas, of which two are as large as

5232-542: The Sanskrit language. It is perhaps best known for its association with Chanakya, also known as Kautilya , the strategist who guided Chandragupta Maurya and assisted in the founding of the Mauryan empire. The Ayurvedic healer Charaka also studied at Taxila. He also started teaching at Taxila in the later period. Pāṇini, the grammarian who codified the rules that would define Classical Sanskrit , has also been part of

5341-557: The Taxila area, though the area was eventually abandoned after the collapse of the Indus Valley civilisation. The earliest settled occupation in Taxila Valley was found at Sarai Khola , located 2 km to the south-west of Taxila Museum , where three radiocarbon dates from Period I suggest the site was first occupied between the late 4th and early 3rd millennium BCE, with deposits of polished stone celts, chert blades and

5450-478: The age of eight), and their secondary education in the Ashrams (between the ages of eight and twelve), and therefore came to Taxila chiefly to reach the ends of knowledge in specific disciplines. The sites of a number of important cities noted in ancient Indian texts were identified by scholars early in the 19th century. The lost city of Taxila, however, was not identified until later, in 1863-64. Its identification

5559-423: The boiling flask 2 is heated by a combined hotplate and magnetic stirrer 13 via a silicone oil bath (orange, 14). The vapor flows through a short Vigreux column 3, then through a Liebig condenser 5, is cooled by water (blue) that circulates through ports 6 and 7. The condensed liquid drips into the receiving flask 8, sitting in a cooling bath (blue, 16). The adapter 10 has a connection 9 that may be fitted to

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5668-430: The boiling point of the mixture to rise, which results in a rise in the temperature in the vapor, which results in a changing ratio of A : B in the gas phase (as distillation continues, there is an increasing proportion of B in the gas phase). This results in a slowly changing ratio of A : B in the distillate. If the difference in vapour pressure between the two components A and B is large – generally expressed as

5777-617: The centuries, with many empires vying for its control. In the 2nd century BCE, Taxila was annexed by the Indo-Greek kingdom of Bactria . Indo-Greeks built a new capital, Sirkap, on the opposite bank of the river from Taxila. During this new period of Bactrian Greek rule, several dynasties (like Antialcidas ) likely ruled from the city as their capital. During lulls in Greek rule, the city managed profitably on its own, to independently control several local trade guilds, who also minted most of

5886-460: The centuries, with many polities vying for its control. When the great ancient trade routes connecting these regions ceased to be important, the city sank into insignificance and was finally destroyed in the 5th century by the invading Hunas . In mid-19th century British India , ancient Taxila's ruins were rediscovered by British archaeologist Alexander Cunningham and extensively excavated by Sir John Marshall . In 1980, UNESCO designated Taxila as

5995-718: The city had come under Kushan rule by that time, after the city was captured from the Parthians by Kujula Kadphises , founder of the Kushan Empire . The great Kushan ruler Kanishka later founded Sirsukh , the most recent of the ancient settlements at Taxila. In the mid-fourth century CE, the Gupta Empire occupied the territories in Eastern Gandhara, establishing a Kumaratya's post at Taxila. The city became well known for its trade links, including silk, sandalwood, horses, cotton, silverware, pearls, and spices. It

6104-505: The city was founded by Bharata , the younger brother of the Hindu deity Rama , and named in honour of Bharata's son, Taksha. The city's modern name, however, is derived from the ancient Greek rendering noted in Ptolemy 's Geography . The Greek-language transcription of Taxila became universally favoured over time, and both the Sanskrit and Pali names fell out of use. Faxian ,

6213-583: The city within seven days without falling prey to the yakshinis who waylaid travellers in the forest. According to the Dipavamsa , one of Taxila's early kings was a Kshatriya named Dipankara who was succeeded by twelve sons and grandsons. Kuñjakarṇa , mentioned in the Avadanakalpalata , is another king associated with the city. In the Jain tradition, it is said that Rishabha , the first of

6322-623: The city's autonomous coinage. In about the 1st century BCE or 1st century CE, an Indo-Scythian king named Azilises had three mints, one of which was at Taxila, and struck coins with obverse legends in Greek and Kharoṣṭhī . The last Greek king of Taxila was overthrown by the Indo-Scythian chief Maues around 90 BCE. Gondophares , founder of the Indo-Parthian Kingdom , conquered Taxila around 20 BCE, and made Taxila his capital. According to early Christian legend, Thomas

6431-612: The city. In a 2010 report, the Global Heritage Fund identified Taxila as one of 12 worldwide sites that were "on the verge" of irreparable loss and damage, citing insufficient management, development pressure, looting, and armed conflict as primary threats. However, significant preservation efforts have since been carried out by the Pakistani government , which has resulted in the site's recategorization as "well-preserved" by different international publications. Because of

6540-821: The community at Taxila. Jīvaka , the court physician of the Magadha emperor Bimbisara who once cured the Buddha, and the Buddhism-supporting ruler of Kosala, Prasenajit, are some important personalities mentioned in Pali texts who studied at Taxila. No external authorities like kings or local leaders subjected the scholastic activities at Taxila to their control. Each teacher formed his own institution, enjoying complete autonomy in work, teaching as many students as he liked and teaching subjects he liked without conforming to any centralised syllabus. Study terminated when

6649-410: The composition of the source material, the vapors of the distilling compounds, and the distillate change during the distillation. In batch distillation, a still is charged (supplied) with a batch of feed mixture, which is then separated into its component fractions, which are collected sequentially from most volatile to less volatile, with the bottoms – remaining least or non-volatile fraction – removed at

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6758-650: The control of Chandragupta Maurya . His advisor, Kautilya/Chanakya , was said to have taught at Taxila's university. Under the reign of Ashoka the Great , Chandragupta's grandson, the city was made a great seat of Buddhist learning, though the city was home to a minor rebellion during this time. Taxila was founded in a strategic location along the ancient "Royal Highway" that connected the Mauryan capital at Pataliputra in Bihar , with ancient Peshawar, Puṣkalāvatī, and onwards towards Central Asia via Kashmir , Bactria, and Kāpiśa . Taxila thus changed hands many times over

6867-545: The desired end products. In the case of oil refining, crude is subjected to a long series of individual distillation steps, each of which produces a different product or intermediate . Taxila Taxila ( Punjabi , Urdu : ٹيکسلا ; Punjabi pronunciation: [ʈɛksɪlaː] ), historically known as Takshashila , is a historic city, located on the Pothohar Plateau , in Punjab, Pakistan . Founded as

6976-917: The development of accurate design methods, such as the McCabe–Thiele method by Ernest Thiele and the Fenske equation . The first industrial plant in the United States to use distillation as a means of ocean desalination opened in Freeport, Texas in 1961 with the hope of bringing water security to the region. The availability of powerful computers has allowed direct computer simulations of distillation columns. The application of distillation can roughly be divided into four groups: laboratory scale , industrial distillation , distillation of herbs for perfumery and medicinals ( herbal distillate ), and food processing . The latter two are distinctively different from

7085-434: The difference in boiling points – the mixture in the beginning of the distillation is highly enriched in component A, and when component A has distilled off, the boiling liquid is enriched in component B. Continuous distillation is an ongoing distillation in which a liquid mixture is continuously (without interruption) fed into the process and separated fractions are removed continuously as output streams occur over time during

7194-401: The domestic production of flower water or essential oils . Early forms of distillation involved batch processes using one vaporization and one condensation. Purity was improved by further distillation of the condensate. Greater volumes were processed by simply repeating the distillation. Chemists reportedly carried out as many as 500 to 600 distillations in order to obtain a pure compound. In

7303-531: The early 19th century, the basics of modern techniques, including pre-heating and reflux , were developed. In 1822, Anthony Perrier developed one of the first continuous stills, and then, in 1826, Robert Stein improved that design to make his patent still . In 1830, Aeneas Coffey got a patent for improving the design even further. Coffey's continuous still may be regarded as the archetype of modern petrochemical units. The French engineer Armand Savalle developed his steam regulator around 1846. In 1877, Ernest Solvay

7412-418: The end. The still can then be recharged and the process repeated. In continuous distillation , the source materials, vapors, and distillate are kept at a constant composition by carefully replenishing the source material and removing fractions from both vapor and liquid in the system. This results in a more detailed control of the separation process. The boiling point of a liquid is the temperature at which

7521-550: The experiment may have been an important step towards distillation. Early evidence of distillation has been found related to alchemists working in Alexandria in Roman Egypt in the 1st century CE. Distilled water has been in use since at least c.  200 CE , when Alexander of Aphrodisias described the process. Work on distilling other liquids continued in early Byzantine Egypt under Zosimus of Panopolis in

7630-564: The extensive preservation efforts and upkeep, Taxila is one of Punjab's popular tourist spots , attracting up to one million tourists every year. In ancient times, Taxila was known as Takṣaśilā in Sanskrit (per IAST ) and as Takkhasilā in Pali . The city's Sanskrit name translates to "City of Cut Stone" or "Rock of Taksha" in reference to a story in the Ramayana that states that

7739-448: The former two in that distillation is not used as a true purification method but more to transfer all volatiles from the source materials to the distillate in the processing of beverages and herbs. The main difference between laboratory scale distillation and industrial distillation are that laboratory scale distillation is often performed on a batch basis, whereas industrial distillation often occurs continuously. In batch distillation ,

7848-475: The great Manikyala tope, twenty eight monasteries, and nine temples. Taxila's archaeological sites lie near modern Taxila about 35 km (22 mi) northwest of the city of Rawalpindi . The sites were first excavated by John Marshall , who worked at Taxila over a period of twenty years from 1913. The vast archaeological site includes neolithic remains dating to 3360 BCE, and Early Harappan remains dating to 2900–2600 BCE at Sarai Kala . Taxila, however,

7957-497: The industrial rather than bench scale of the operation. As alchemy evolved into the science of chemistry , vessels called retorts became used for distillations. Both alembics and retorts are forms of glassware with long necks pointing to the side at a downward angle to act as air-cooled condensers to condense the distillate and let it drip downward for collection. Later, copper alembics were invented. Riveted joints were often kept tight by using various mixtures, for instance

8066-429: The liquid state , and a receiver in which the concentrated or purified liquid, called the distillate, is collected. Several laboratory scale techniques for distillation exist (see also distillation types ). A completely sealed distillation apparatus could experience extreme and rapidly varying internal pressure, which could cause it to burst open at the joints. Therefore, some path is usually left open (for instance, at

8175-445: The long and arduous journey they had to undergo, on account of the excellence of the learned teachers there, all recognised as authorities on their respective subjects. The admission to Takshashila was not only limited to the students belonging to the elite class, some evidence mentions the sons of kings, nobles, merchants, tailors, and even fishermen getting education at Takshashila. Taxila had great influence on Hindu culture and

8284-411: The mixture to have a zero partial pressure . If ultra-pure products are the goal, then further chemical separation must be applied. When a binary mixture is vaporized and the other component, e.g., a salt, has zero partial pressure for practical purposes, the process is simpler. Heating an ideal mixture of two volatile substances, A and B, with A having the higher volatility, or lower boiling point, in

8393-411: The more volatile compound, A (due to Raoult's Law, see above). The vapor goes through the condenser and is removed from the system. This, in turn, means that the ratio of compounds in the remaining liquid is now different from the initial ratio (i.e., more enriched in B than in the starting liquid). The result is that the ratio in the liquid mixture is changing, becoming richer in component B. This causes

8502-787: The old world until the destruction of the city in the 5th century. It has been suggested that at its height, Taxila exerted a sort of "intellectual suzerainty " over other centres of learning in India and its primary concern was not with elementary, but higher education. Generally, a student entered Taxila at the age of sixteen. The ancient and the most revered scriptures, and the Eighteen Silpas or Arts, which included skills such as archery, hunting, and elephant lore, were taught, in addition to its law school, medical school, and school of military science . Students came to Taxila from far-off places such as Kashi , Kosala and Magadha, in spite of

8611-432: The operation. Continuous distillation produces a minimum of two output fractions, including at least one volatile distillate fraction, which has boiled and been separately captured as a vapor and then condensed to a liquid. There is always a bottoms (or residue) fraction, which is the least volatile residue that has not been separately captured as a condensed vapor. Continuous distillation differs from batch distillation in

8720-413: The principles are the same. Examples of laboratory-scale fractionating columns (in increasing efficiency) include: Laboratory scale distillations are almost exclusively run as batch distillations. The device used in distillation, sometimes referred to as a still , consists at a minimum of a reboiler or pot in which the source material is heated, a condenser in which the heated vapor is cooled back to

8829-434: The receiving flask) to allow the internal pressure to equalize with atmospheric pressure. Alternatively, a vacuum pump may be used to keep the apparatus at a lower than atmospheric pressure. If the substances involved are air- or moisture-sensitive, the connection to the atmosphere can be made through one or more drying tubes packed with materials that scavenge the undesired air components, or through bubblers that provide

8938-490: The region in 326 BCE. The third and most recent settlement is that of Sirsukh , which was built by rulers of the Kushan empire, who ruled from nearby Purushapura (modern Peshawar ). Taxila was designated a UNESCO World Heritage Site in 1980 in particular for the ruins of the four settlement sites which "reveal the pattern of urban evolution on the Indian subcontinent through more than five centuries". The serial site includes

9047-545: The region of Gandhara . In later Buddhist texts, the 4th - 3rd century BCE Jatakas , it is specified that Taxila was the city where Aruni and his son Shvetaketu each had received their education. One of the earliest mentions of Taxila is in Pāṇini 's Aṣṭādhyāyī , a Sanskrit grammar treatise dated to the 4th century BCE. Much of the Hindu epic, the Mahabharata , is a conversation between Vaishampayana (a pupil of

9156-428: The respect that concentrations should not change over time. Continuous distillation can be run at a steady state for an arbitrary amount of time. For any source material of specific composition, the main variables that affect the purity of products in continuous distillation are the reflux ratio and the number of theoretical equilibrium stages, in practice determined by the number of trays or the height of packing. Reflux

9265-403: The rising vapors into close contact with the descending condensate, increasing the number of theoretical plates. Separation process Processes are often classified according to the particular properties they exploit to achieve separation. If no single difference can be used to accomplish the desired separation, multiple operations can often be combined to achieve the desired end. With

9374-536: The rule of the Persian Achaemenid Empire in the 6th century BCE. In 516 BCE, Darius I embarked on a campaign to conquer Central Asia , Ariana and Bactria , before marching onto what is now Afghanistan and northern Pakistan . Emperor Darius spent the winter of 516-515 BCE in the Gandhara region surrounding Taxila, and prepared to conquer the Indus Valley , which he did in 515 BCE, after which he appointed Scylax of Caryanda to explore

9483-539: The sage, Vyasa ) and King Janamejaya . It is traditionally believed that the story was first recited by Vaishampayana at the behest of Vyasa during the snake sacrifice performed by Janamejaya at Takshashila. The audience also included Ugrashravas , an itinerant bard, who would later recite the story to a group of priests at an ashram in the Naimisha Forest from where the story was further disseminated. The Kuru Kingdom 's heir, Parikshit (grandson of Arjuna)

9592-418: The separation process of distillation exploits the differences in the relative volatility of the component substances of the heated mixture. In the industrial applications of classical distillation, the term distillation is used as a unit of operation that identifies and denotes a process of physical separation, not a chemical reaction ; thus an industrial installation that produces distilled beverages ,

9701-443: The separation processes of destructive distillation and of chemical cracking , breaking down large hydrocarbon molecules into smaller hydrocarbon molecules. Moreover, a partial distillation results in partial separations of the mixture's components, which process yields nearly-pure components; partial distillation also realizes partial separations of the mixture to increase the concentrations of selected components. In either method,

9810-435: The social, intellectual and moral atmosphere there. Knowledge was considered too sacred to be bartered for money, and hence any stipulation that fees ought to be paid was vigorously condemned . Financial support came from the society at large, as well as from rich merchants and wealthy parents . Though the number of students studying under a single Guru sometimes numbered in the hundreds, teachers did not deny education even if

9919-421: The solution and 2) the fraction of solution each component makes up, a.k.a. the mole fraction . This law applies to ideal solutions , or solutions that have different components but whose molecular interactions are the same as or very similar to pure solutions. Dalton's law states that the total pressure is the sum of the partial pressures of each individual component in the mixture. When a multi-component liquid

10028-408: The student was poor; free boarding and lodging was provided, and students had to do manual work in the household . Paying students, such as princes, were taught during the day, while non-paying ones were taught at night. Gurudakshina was usually expected at the completion of a student's studies, but it was essentially a mere token of respect and gratitude - many times being nothing more than a turban,

10137-432: The teacher was satisfied with the student's level of achievement. In general, specialisation in a subject took around eight years, though this could be lengthened or shortened in accordance with the intellectual abilities and dedication of the student in question. In most cases the "schools" were located within the teachers' private houses, and at times students were advised to quit their studies if they were unable to fit into

10246-461: The teachers living there may not have had official membership of particular colleges, and there did not seem to have existed purpose-built lecture halls and residential quarters in Taxila, in contrast to the later Nalanda university in eastern India. Taxila became a noted centre of learning (including the religious teachings of Historical Vedic Religion and Buddhism ) at least several centuries BCE, and continued to attract students from around

10355-420: The twelfth century, recipes for the production of aqua ardens ("burning water", i.e., ethanol) by distilling wine with salt started to appear in a number of Latin works, and by the end of the thirteenth century it had become a widely known substance among Western European chemists. The works of Taddeo Alderotti (1223–1296) describe a method for concentrating alcohol involving repeated distillation through

10464-400: The vapors of each component to collect separately and purely. However, this does not occur, even in an idealized system. Idealized models of distillation are essentially governed by Raoult's law and Dalton's law and assume that vapor–liquid equilibria are attained. Raoult's law states that the vapor pressure of a solution is dependent on 1) the vapor pressure of each chemical component in

10573-531: The word distillare (to drip off) when used by the Romans, e.g. Seneca and Pliny the Elder , was "never used in our sense". Aristotle knew that water condensing from evaporating seawater is fresh: I have proved by experiment that salt water evaporated forms fresh, and the vapour does not, when it condenses, condense into sea water again. Letting seawater evaporate and condense into freshwater can not be called "distillation" for distillation involves boiling, but

10682-559: The works attributed to Jābir, such as in the Kitāb al-Sabʿīn ('The Book of Seventy'), translated into Latin by Gerard of Cremona ( c.  1114–1187 ) under the title Liber de septuaginta . The Jabirian experiments with fractional distillation of animal and vegetable substances, and to a lesser degree also of mineral substances, is the main topic of the De anima in arte alkimiae , an originally Arabic work falsely attributed to Avicenna that

10791-464: Was applied to any process where a liquid was separated in drops. To distil in the modern sense could only be expressed in a roundabout manner. Distillation had a broader meaning in ancient and medieval times because nearly all purification and separation operations were subsumed under the term distillation , such as filtration, crystallization, extraction, sublimation, or mechanical pressing of oil. According to Dutch chemical historian Robert J. Forbes ,

10900-440: Was critical and thorough- unless one unit was mastered completely, the student was not allowed to proceed to the next . No convocations were held upon completion, and no written "degrees" were awarded, since it was believed that knowledge was its own reward. Using knowledge for earning a living or for any selfish end was considered sacrilegious. Students arriving at Taxila usually had completed their primary education at home (until

11009-430: Was established around 1000 BCE. By 900 BCE, the city was already involved in regional commerce, as the discovered pottery shards reveal trading ties between the city and Puṣkalāvatī . Later, Taxila was inhabited at Bhir Mound , dated to some time around the period 800-525 BCE with these early layers bearing grooved red burnished ware. Archaeological excavations show that the city may have grown significantly during

11118-572: Was for a time the capital city of ancient Gandhāra , situated on the eastern shore of the Indus River —the pivotal junction of the Indian subcontinent and Central Asia ; it was possibly founded around 1000 BCE. The city was part of the Achaemenid empire's Hindush colony, between ~550 - 326 BCE. In 326 BCE, the city was conquered by Alexander the Great who gained control of the city without

11227-399: Was granted a U.S. Patent for a tray column for ammonia distillation, and the same and subsequent years saw developments in this theme for oils and spirits. With the emergence of chemical engineering as a discipline at the end of the 19th century, scientific rather than empirical methods could be applied. The developing petroleum industry in the early 20th century provided the impetus for

11336-525: Was known in the 19th century as Babur Khana ('House of Tiger'), alluding to the place where Gautama Buddha had offered his head. In addition, a hill range to south of the Taxila Valley is called Margala ( lit.   ' cut-off throat ' ). In Vedic texts such as the Shatapatha Brahmana , it is mentioned that the Vedic philosopher Uddalaka Aruni (c. 7th century BCE) had travelled to

11445-625: Was made difficult partly due to errors in the distances recorded by Pliny in his Naturalis Historia which pointed to a location somewhere on the Haro river , two days march from the Indus . Alexander Cunningham , the founder and the first director-general of the Archaeological Survey of India , noticed that this position did not agree with the descriptions provided in the itineraries of Chinese pilgrims and in particular, that of Xuanzang,

11554-580: Was no efficient means of collecting the vapors at low heat. Distillation in China may have begun at the earliest during the Eastern Han dynasty (1st–2nd century CE). Medieval Muslim chemists such as Jābir ibn Ḥayyān (Latin: Geber, ninth century) and Abū Bakr al-Rāzī (Latin: Rhazes, c.  865–925 ) experimented extensively with the distillation of various substances. The fractional distillation of organic substances plays an important role in

11663-467: Was replaced by the Hindu Shahi dynasty which was overthrown by Mahmud of Ghazni with the defeat of Trilochanpala . Al-Usaifan's king during the reign of Al-Mu'tasim is said to have converted to Islam by Al-Biladhuri and abandoned his old faith due to the death of his son despite having priests of a temple pray for his recovery. Said to be located between Kashmir, Multan and Kabul, al-Usaifan

11772-494: Was translated into Latin and would go on to form the most important alchemical source for Roger Bacon ( c.  1220–1292 ). The distillation of wine is attested in Arabic works attributed to al-Kindī ( c.  801–873 CE ) and to al-Fārābī ( c.  872–950 ), and in the 28th book of al-Zahrāwī 's (Latin: Abulcasis, 936–1013) Kitāb al-Taṣrīf (later translated into Latin as Liber servatoris ). In

11881-479: Was visited by him in 630 CE, and found most of its sangharamas still ruined and desolate. Only a few monks remained there. He adds that the kingdom had become a dependency of Kashmir with the local leaders fighting amongst themselves for power. He noted that it had some time previously been a subject of Kapisa . By the ninth century, it became a dependency of the Kabul Shahis. The Turki Shahi dynasty of Kabul

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