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 DOMINION OF CANADA 
 
 THE HONORARY ADVISORY COUNCIL FOR SCIENTIFIC 
 AND. INDUSTRIAL RESEARCH 
 
 REPORT No. 2 
 
 THE RECOVERY OF 
 VAPOURS FROM GASES 
 
 Particularly of Benzene and Toluene 
 from Coal Gas 
 
 By 
 
 HAROLD S. DAVIS. M.A.. Ph. D.. 
 
 and 
 
 MARY DAVIDSON DAVIS, B.A. 
 
 Canaba 
 
 Published by the authority of the Sub-Conunittee of the Privy 
 Council for Scientific and Industrial Research 
 
 OTTAWA, 1918 
 
DOMINION OF CANADA 
 
 THE HONORARY ADVISORY COUNCIL FOR SCIENTIFIC 
 AND INDUSTRIAL RESEARCH 
 
 REPORT No. 2 
 
 THE RECOVERY OF 
 VAPOURS FROM GASES 
 
 Particularly of Benzene and Toluene 
 from G)al Gas 
 
 By 
 
 HAROLD S. DAVIS, M.A., Ph. D.. 
 
 and 
 
 MARY DAVIDSON DAVIS, B.A. 
 
 Canaba 
 
 Published by the authority of the Sub-Gmimittee of the Privy 
 Council for Scientific and Industrial Research 
 
 OTTAWA, 1918 
 
TABLE OF CONTENTS. 
 
 PAGE. 
 
 3 
 
 I Prefack 
 
 3 
 
 II iNTRODtCTION 
 
 Destructive Distillation of Coal 
 
 Recovery of " Light Oils " from Coal Gas 4 
 
 The Relation between Maximum Enrichment at 1 the 
 
 Composition of the Oil ^ 
 
 The Extraction of Toluene only from Coal Gas 9 
 
 III A New Method for the Quantitative Estimation of 
 
 Vapours in Gases • 1" 
 
 Theory of Method ^^ 
 
 Experimental Part 
 
 Efficiency of Method ^^ 
 
 The Estimation of the Benzene Content of Coal Gas .... 13 
 Contents of the Rich and Poor Washing Oils 14 
 
 14 
 
 IV Conclusion 
 
 V List of Previous Publications on the Subject by the 
 Authors 
 
 00937797 
 
I. PREl ACE. 
 
 This bulletin is not intended to be a <=°'"P;f f"\'^'^„J'",\*i^,°S 
 "benzol recovery." It embodies the main resu ts oJ researcn 
 cSout for two sessions, 1916-18. in the University of Man'toba. 
 wTth some reference to practical testscarried out on the Light Od 
 Recoverv Plant of the toronto Chemical Co., at Sault Stc. Mane. 
 oSt lilostof the results of this rese.'ch have a ready b^nput^^ 
 Zuh fuller details in the papers listed on page IS, but it is nopea in 
 rhil^Setiulo Resent fhe conclusions and their significance in a 
 
 ^"' We" wish to"acknowledge the substantial grant given by the 
 
 Adviso^ Council to aid the prosecution of this work during the 
 
 :^«7qi 7 1 H This crant was used to secut* as a research assistant 
 
 S Donal^i mIS?. who has been intimately associate with 
 
 the work. 
 
 II. INTRODUCTION. 
 
 The number of problems arising from the tremendous impetus 
 given the pr(3uction of benzene and toluene since the year 1914. led to 
 the investigations outlined in this paper. r,^,:„„ -«■ 
 
 Benzene is a colourless liquid boiling at about 80° and freezing at 
 oKoMt rs" wtth a soecific gravity of 0-87. On account of its theo- 
 ?et°cal and pmairaSporta^ce. it holds a place almost unique among 
 ocean ccl^poun^^^^ It is the basic substance from which the greater 
 narfof organic compounds constituting what is known as the aromatic 
 series may be considered to be derived Many o these compounds 
 such arphenol and aniline are actual y «y"*hes«ed from it on a 
 commercial scale, while great quantities ^'^ ,"«f J^j'^f^^f'^p^;. 
 facture of high explosives. It makes an excellent "\otor tuei. par 
 ttuSrlv when certain suitable organic liquids are dissolved in it. 
 Cerine iu freezing pomt and also preventing the deposition of carbon 
 IrthTc^Hnders cLmercial fuels such as " bengas are formed m 
 
 ^^'^ Tohiene is also a liquid, of a somewhat higher boiling point and 
 lowe7free'^ng poin? than benzene. It is used • . large quantities m the 
 manufacture of the high explosive, trinitrotouene. 
 
 The inCTease in the number of industries conceriied with th^ 
 manufactir"of these substances since the beginning of the war ha ^1^ 
 to an overproduction of benzene in America; the supply of toluene, 
 
 '""Tesl^Si^^liSin^ce^^^^^^^^^^^ and toluene, are mainly obtained 
 .s by-products from the d-' tructive distillation of coal. 
 
 THE DESTRUCTIVE DISTILLATION OF COAL. 
 
 When coal is heated in a closed space with f^J e^J=|"ded. it 
 undergoes decomposition and a great many chemical substances are 
 formed At ordinary temperatures some of these are solids, others 
 v^A^' a«^ manv irases Aereat deal of solid material remains in the 
 'ZninTco':^^^^ke''^^ml.tur. of other substances formed 
 
 4521(V-1| 
 
in ereat volume is drawn of! from the coke ovens. The ««"»tfJ Pf/* °S 
 hifgt. mixture is composed of such permanent k;-*».^ "^^Jj'^^^^^^^t 
 carbSn monoxide, but it also contams smalljuant.t^ o a JUng- 
 number of liquids and solids of various boilmg pomts. As it is cooiw, 
 Mrtial condensation takes place, and one or more complex solutions 
 JSiar At Cr^ iary temjLatures. at least two solutions separate 
 oSrone com^ Urgely^water. known "^^^rnmontacalliquor^he 
 oSir madHrX grelt number of organic substances and known by 
 
 '""^ 'lTwo!,rdX''aTundamental mistake, however, to -upm^ that 
 some subices completely condense into the ».<? "Jjon wh. e^o^^^^^^ 
 pass along in the gas. Rather, each substance distributes itself in a 
 certain ratio between the gaseous and liquid phascs. 
 
 About 1-2 p.c. by volume of the gases from V^e coke ovens is 
 com^ < 1 co'mpou^ds of the aromatic -ries. ch.efly the hydro- 
 carboi^such as Ix^nzene and toluene. They are the chiet con 
 stituents of what is technically called the ight oil 
 
 Of course a certain amount of these substances stays in the tar^ 
 especiaUy if it is «parated from the gas at a low temperature; inde^ 
 Srmanv vears tar was their chief source. But by far the greater 
 cuamityonhe light oils remains in the coal gas. even after it has been 
 SKth watir or otherwise purified. The ratio of the amounts in 
 
 *'^ ^xL^loun'tTea^h of'^hele vapours in the gas is far below it. 
 »aturi?ron concentration, i.e. the concentration '" «lH}!'b"""^j;*JhJS 
 mire solid or liquid substance at that temperature. To separate tnese 
 Saooms from ?he gas. two main methods have been employed :- 
 vapours iromtneg.^^ and compressed so that the concentration of 
 
 the vapours is brought above saturation and they separate out a 
 
 "''"'?The vapours are absorbed into a high boiling oil. from which 
 thev are subsequently separated by »<-stillation. 
 
 ^The first method has never been a success commercially: the 
 latter is the one universally employed. 
 
 THE RECOVERY OF " LIGHT OILS " FROM COAL GAS. 
 
 The theory of the washing process may perhaps be more readily 
 understo^ if we consider the extraction of one vapour only, e.g. 
 
 ^Tonir a\"bS:ofgSTtrrfiStrpressure and tem.perature. 
 surround'^ by a pu?ew^^^^^^^ HQ^id- The bcr.zene vapour in the gas 
 wm d^LoWe in the oil until the vapour p.cssure of benzene fron. the 
 Tu^ounding oil is equal to that in the gas. So the maximum content 
 of Wene which can be absorbed by the oil from the gas is that which 
 riv^a va^ur p^^^ -f benzene from the solution equal to the vapour 
 weSure Sf beSzene in the gas. Consider a counter-current washing 
 svSrsuchasIs represented in Fig. 1. for washing the gas con- 
 dniously with oi . The gas passing through the system meets the oi 
 travS.^ he opposite direction. Fresh oil takes out the last traces of 
 bSSne f rom the gas. since such oil has no vapour pressure of benzene^ 
 The on thereby acquires a vapour pressure of benzene proportional to 
 
ur«i«.t. vaa with a h Kher apour preMure of beniene until it couia 
 eave witK v^Zr p SSre oTb*n«ne equal to that in the rich ga. 
 Intering -nie Sn« i« •epa'atcd by distillation from the oil and th. 
 
 •^"'^tI: :;r^o5^-£. of 'r^ene fr.n the ga. there are 
 
 *"°';'^7oru«rtw«n ga. and oil in the ^.rubber. n.u.t be 
 
 -'^TlVr^e^rBt^o^r'Lrr.t^^ 
 
 quantity of l^nzene. carried from the washer, per «.cond. .hall be 
 equal to the quantity brought in by the gas. 
 
 <v'veralimDortant points should be noted here:— 
 L Iffust tCt amount of oil is passed through the w^v^erj which 
 is necessaW to completely remove all the^^^^^^ 
 thp vanour oressure of benzene from the oi Tiergmj^i "•»- 
 
 fSSy'tfS ■■ rich oil ") will be »u»' - .V^f " r'™ if teU ofl 
 ill the benzene will have been washed fiVi.. the poor ^as. u l«» on 
 
 V "^t^n t^cirrt:';%Tte'^;n»U'tieveT,''w^ 
 ^'iXlg" in thi'^r PnS'thete is noAsufficiej, oil to remove 
 it Finally, if more oil than necessary is used, all the J^eMene win 
 fc removed from the poor gas. but the vapour pressure from the rich 
 
 ^■'^"i" inri^dli^^'Vo'fompSet^^^^^^^^ an the benzene from 
 
 the gas the iow^^^ shouTdX soi^ewhat greater than the amount 
 thLretlcally necessary, so that the vapour pressure of bfn"n«"lJ£^ 
 Srill always be grSier than its vapour pressure from the oil- Jhis 
 SLiTentoT vapour pressure will tend to dissolve the benzene fromjhe 
 faSo the oil The more nearly perfect the wash.n , system the smaller 
 
 5 
 
this gradient need be. On the other hand, a very inefficient washing 
 system will extract all the benzene if sufficient oil is passed through the 
 scrubbers. However, since the chief cost in lx;nzene recovery is 
 concerned with the separation of the benzene from the rich oil, it is 
 desirable to use as little washing oil as possible. 
 
 3. In order to completely remove the benzene from the gas, the 
 poor oil which enters the scrubbers must be completely free from 
 benzene, for no amount of washing will ever lower the vapour pressure 
 in the poor gas below that of the poor oil with which it is finally washed. 
 The presence of benzene in the poor oil means that the steam dis- 
 tillation is inefficient, and does not completely separate the benzene 
 from the washing oil. Such inefficiency may cause a very serious 
 loss to the plant, for the fraction of benzene lost will be the ratio of the 
 vapour pressure of benzene from the poor oil to that in the rich gas. 
 Later in this paper, methods of measuring this ratio will be described. 
 
 THE RELATION' BETWEEN MAXIMUM ENRICHMENT AND THE 
 COMPOSITION OF THE OIL. 
 
 From what has preceded it w''.l be plain that the rnaximum 
 enrichment of benzene which the oil can assume is the quantity which 
 will give a vapour pressure of benzene equal to the vapour pressure of 
 benzene in the gas. Hence the maximum enrichment will depend 
 upon the content of the gas and the pressure upon it. In order to 
 determine the other factors governing this maximum enrichment, we 
 carried out a series of experiments in which we measured the vapour 
 pressure of benzene from solutions in washing oil, using diflferent con- 
 centrations and different temperatures. The results obtained may be 
 summarized as follows : — 
 
 1. The vapour pressure of benzene at 33 • 2° from two solutions in 
 oil, one of approximately double the concentration of the other, was 
 directly proportional to the concentration That is to say, the vapour 
 pressure of benzene from a solution in oil, and the concentration of 
 benzene in the oil are related according to Henry's Law for the 
 solubility of gases in liquids— a result of great theoretical and prac- 
 tical importance. 
 
 2. The ratio of the vapour pressure of benzene from a solution of 
 definite concentration to its saturation pressure was independent of 
 the temperature. (Von Babo's Law.) 
 
 It is thus possible to calculate the vapour pressure of benzene from 
 a solution of any particular concentration at any temperature, since 
 the vapour pressure of pure benzene is known at that temperature and 
 also the ratio borne to it by the vapour pressure from a 1 p.c. solution 
 in oil. 
 
 The amount of fresh washing oil required for any particular rate 
 of flow of gas depends only on the temperature of washing. The 
 benzene content of the gas does not affect it; for if this content is 
 increased, then the maximum content in the rich oil is increased in the 
 same proportion. 
 
 Now the efficiency of an oil for absorbing benzene from gases is 
 determined by the magnitude of the vapour pressure of benzene from its 
 solution in the oil, or to look at it from another point of view, the 
 efficiency of an oil is determined by its power to lower the vapour 
 
pressure of benzene when dissolved in it. For dilute solutions in 
 common solvents, this power of lowering the vapour pressure is in- 
 versely proportional to the molecular weight of the dissolved sub- 
 stance, so that if the molecular concentration of the solution is known, 
 the proportional lowering of the vapour pressure of the solvent can be 
 calculated from a well-known formula. Since benzene and the 
 washing oil used were soluble in all proportions we suspected that 
 this relation might hold for very concentrated solutions; results con- 
 firmed this supposition. • . u ^. 
 
 The average molecular weight of the oil determined by the 
 freezing point method was found to be 205. From this, the vapour 
 pressure from a 99 p.c. solution of oil in benzene, i.e. a 1 p.c solution 
 of benzene in oil, was calculated to be 0263, in excellent agreement 
 with the experimental result 026. •, u ^• 
 
 The determination of the molecular weight of an oil when dis- 
 solved in benzene seems therefore to afford a good method for testing 
 the efficiency of the oil for absorbing benzene or other vapours from 
 gases; the lower the molecular weight, the greater the efficiency. 
 
 A few tests were made on absorbing oils used at a light-oil 
 recovery plant, in order to ascertain if this method of standardization 
 would hold. In general it was found that oils of low molecular 
 weight, 200-230, were good absorbers in practice, while an oil with 
 a much higher molecular weight, 280, had been rejected as inefficient. 
 It is hoped that research may lead to the development of washing 
 media with lower molecular weights than those of the present absorbers, 
 which at the same time will have the desired qualities of fluidity, 
 
 boiling point, etc. i r tu 
 
 So far we have considered the removal of one vapour only trom tne 
 gas. Similar considerations apply to the removal of a mixture of 
 vapours such as those which make up the " light oils. 
 
 In considering the process of absorption of light oils into washing 
 oil, account must be taken of the following premises, experimental 
 confirmation of which is cited further on in the paper: — 
 
 1. Each separate vapour contained in the gas dissolves in the 
 washing oil, independently of the other vapours present, until equili- 
 brium is reached between its vapour pressure in the gas and its vapour 
 pressure from the oil solution. 
 
 2. \\ hf-n washing of moderate efficiency is employed, equilibrium 
 between the oi' and each of the light oil vapours is reached much more 
 quickh- than lias often been supposed. . . u 
 
 Of course each of the constituents of the gas, other than the 
 light oils, also dissolves in the washing medium until corresponding 
 equilibrium is reached, but the amount dissolved is so small that its 
 effect may be neglected. 
 
 Now, although the oil constantly absorbs vapours from the gas, 
 equilibrium between the vapour pressures of each substance m the gas 
 and from the oil being closely maintained at every stage, it does not 
 follow that the oil becomes saturated with every vapour at the same 
 stage of washing. Rather, the stage at which the oil becomes satur- 
 ated with respect to any one vapour is determined by the saturation 
 pressure of the pure liquid of the same composition as the vapour in 
 <luestion. 
 
Consider now the absorption of benzene and toluene vapoura 
 from the gas into the washing oil. The benzene content in the rich 
 oil will be at its maximum when it. gives a vapour pressure of benzene 
 equal to that in the rich gas. At this stage the dissolved toluene 
 only gives a pressure from the oil equal to a fraction of the toluene 
 pressure in the rich gas. This fraction can be shown to be equal to the 
 ratio of the saturation pressure of pure toluene to that of pure benzene, 
 so that when the oil is saturated with benzene it is only ^ saturated 
 with toluene. Any attempt to obtain a higher percentage of toluene 
 in the rich oil will result in loss of benzene, for some will pass now 
 through unabsorbed. 
 
 If by the maximum enrichment of the washing oil is meant 
 the maximum quantity of light oil which it can contain, without any 
 light oil passing through unabsorbed, then it is reached when the 
 vapour pressure from the washing medium of the lowest boiling com- 
 pound in the light oil, in this case benzene, is equal to its pressure in 
 the rich gas. 
 
 From the equation for the lowering of the vapour pressure 
 referred to above, using an oil with an average molecular weight 
 205, the following calculations can be made for a gas with a vapour 
 pressure of benzene of ■ 6 cm. and of toluene of ■ 15 cm. : — 
 
 1. The possible concentration in oil at 26° for benzene is 2 • 3 p.c. 
 and for toluene 2-3 p.c. 
 
 2. When the oil is saturated with benzene, it will have taken up 
 only 0-68 p.c. of toluene. 
 
 The addition of the toluene (mol. wt. 92) will also lower tho 
 the average molecular weight of the solution in which the benzene is 
 dissolved, thereby increasing the possible concentration of benzene. 
 
 Similar considerations apply to the small quantities of high-boil- 
 ing compounds which exist in the gas and which are soluble in the oil. 
 These factors would result in a steady slow increase in the amount of 
 the total hydrocarbons absorbed, over a comparatively long period. 
 
 To test these conclusions, the following experiments were carried 
 out :^- 
 
 1. Two flasks were filled with known weights of absorbing oil, and 
 illuminating gas was passed through them for a period of two months, 
 the gain in weight being recorded daily. 
 
 2. Two.flasks filled with absorbing oil were connected in series to 
 the gas supply, and the gain in weight of each recorded at certain 
 equal intervals. 
 
 In the case of 1 the following results were obtained : — 
 
 (a) The curves plotted to represent the gain in weight of the 
 flasks rose quite sharply at first, then gradually fell off. At the end of 
 the time the greatest gain in weight of the oil was 5 p.c, with the curve 
 still rising. 
 
 (b) After the curves began to fall off, due undoubtedly to the 
 fact that the benzene was no longet being absorbed from the gas, they 
 began to fluctuate with changes in atmospheric pressure. A low 
 pressure would lessen the concentration of benzene in the gas, so that 
 the -^il would give up some of its benzene to the gas. When this 
 amount was greater than the amount of higher-boiling compounds still 
 being absorbed from the gas, the result was a loss in weight of the oil. 
 
 8 
 
The same result would follow a rise in temperature of the absorbing 
 
 flasks. 
 
 In the case of 2 the results were:— 
 
 (a) The second flask did not begin to gain in weight until there 
 was a perceptible vapour pressure of the light oils from the first flask. 
 
 (b) When the pressure on the second flask was increased, an 
 immediate gain in weight was recorded. When the extra pressure 
 was taken off, the weight immediately fell off again. 
 
 To sum up, our experiments showed : — 
 
 1. Equilibrium was closely maintained between the vapour pres- 
 sure from the oil and that from the gas, although the washing was 
 not particularly efficient. 
 
 2. The oil continued to gain in .veight long after it had reached 
 its maximum benzene content, and this increase in weight continued 
 ovei a very long period. 
 
 THE EXTRACTION OF TOLUENE ONLY FROM COAL GAS. 
 
 The shortage of toluene and the overproduction of benzene have 
 brought up in this country the question raised some time ago in 
 Europe as to whether it is possible to obtain all the toluene from the 
 gas without extracting all the benzene. As has been pointed out 
 already, it is theoretically possible to extract any of the constituents 
 from the gas, provided the proper amount of oil is used. 
 
 In any washing system the absorption process is really selective, 
 some of the constituents being wholly extracted, others only partially. 
 The rich oil is always saturated with respect to the latter. Since the 
 vapour pressure of pure toluene is considerably less than the vapour 
 pressure of pure benzene, it follows that much less oil is required to 
 completely remove the toluene than to completely remove the ben- 
 zene. It is only necessary to have that quantity of oil which will 
 give a vapour pressure of toluene equal to that in the rich gas. This 
 quantity of oil will also remove all the xylenes and other high-boiling 
 constituents, but will only partially extract the benzene. 
 
 Experiments conducted at absorption plants, however, have 
 shown that if the flow of oil is much below that required to nearly 
 extract all the benzene, the toluene yield of the plant is decreased. 
 The following reasons may be given for this decrease in the yield of 
 toluene : — 
 
 1. If the scrubbing system is inefficient, a considerable excess of 
 oil over the amount theoretically required is necessary in order _to 
 provide a solution gradient for the toluene, as previously described for 
 benzene. 
 
 2. The steam stills for separating the light oils may not be 
 efficient and may leave a certain vapour pressure of toluene in the poor 
 oil. As has already been pointed out in the case of benzene, the 
 proportion of toluene lost will be in the direct proportion of the vapour 
 pressure of toluene from the poor oil to that in the rich gas. Now, the 
 time occupied by any quantity of oil in passing down the steam still is 
 fixed, as is the amount of heating and the quantity of steam to which it 
 is exposed. We may therefore assume that as the amount of toluene 
 in the rich oil is decreased, the amount left in the poor oil will also be 
 
decreased. Hence, with an excess of oil, the poor oil coming from the 
 still will contain but little toluene, so that the amount left in the poor 
 gas will be correspondingly small. The result is a comparatively high 
 yield of toluene. The steam distillation still is therefore a very 
 important part of a light-oil recovery plant; nothing can compen- 
 sate for its inefficiency. 
 
 III. A NEW METHOD FOR THE QUANTITATIVE ESTI- 
 MATION OF VAPOURS IN GASES. 
 
 A great need has been felt, by those engaged in the commercial 
 production of light oils, for methods of gas analysis requiring only 
 small samples and giving a rapid estimation of the content of these 
 vapours either collectively or individually. Such methods would make 
 it possible to find the conditions of production necessary to obtain the 
 maximum concentration of each aromatic substance, and would also 
 permit the efificiency of absorption processes to be checked at every 
 point. 
 
 Methods at present employed require the absorption of the light- 
 oil vapours from the gas over a comparatively long period, so that the 
 results represent the average values for this period. Such a method 
 is wholly unsuitable for checking the efficiency of the different parts 
 of the washing system, since conditions such as the rate of flow of the 
 gas, its composition, the temperatures of the washing towers, etc., are 
 continually changing. 
 
 We have developed a new method for the quantitative estimation 
 of vapours in gases, which requires only a s lall sample of gas, 150-350 
 cc and which can be carried to completioii m ^-l hr. 
 
 THEORY OF METHOD. 
 
 It is a generally accepted principle that the vapour pressure from a 
 liquid is independent of the kind of gas above it, provided the gas is 
 inert. Deviatiijiis from this law are well known, but it holds with 
 surprising accuracy in th^ case of a mixture of benzene and air at 
 atmospheric pressure. 
 
 Consider tw.v clos-fl flasks, as in Fig. 2, connected by a mano- 
 meter and filled with r 'r at atmospheric pressure. If now a small 
 sealed bulb conta.ning a v'i., i'j liquid be broken in each, the liquid 
 will partially evaporate, j\A 'i the temperatures of the flasks remain 
 the same, the same additicnal y^ssure will be developed in each, so 
 that the manometer connect i:^ 'hem will register no difference in 
 pressure. Ev en if the tempcratinx^ of the flasks do vary, no difference 
 in pressure will be recorded urtil there is a relative diffe^^ence in 
 temperature between them. 
 
 Now, suppose that one of the flasks had contained a certain 
 quantity of the \ apour of the volatile liquid corresponding to a pressure 
 less tnan the saturation nressuiC. Wli ..» ihe small bulb of liquid was 
 broken in this ono, the liquid wo'iki nor ~iud all its vapour pressure to 
 the pressure already ir the flark, fo ■ p-xri of that was already due to its 
 vapor. It would add only the amount of pressure necessary to bring 
 its pressure up to SwiKa.ion, i. ' si'i.yj the total saturation pressure 
 
was added to the pure air - the other flask, the manometer connecting 
 the two would register a pressure equal to the pressure of vapour in the 
 original gas. The following points are of especial importance : — 
 
 1. Each of the sealed bulbs must contain considerably more 
 liquid than is required, at the temperature cf the experiment, to 
 saturate the atmosphere of the flask into which it is broken with the 
 vapour in question. 
 
 2. It is essential that the substances remaining in the bottoms of 
 the flasks after the bulbs are broken shall have the same composition 
 and shall give the same pressure of the vapour in question, and that 
 this pressure shall be greater than the original pressure of the - apour in 
 the gas. ... ' 
 
 3. A solid can be used in the bulbs in place of a liquid, if the 
 substance exists as a solid at the temperatu-e of the experiment. 
 
 4. A solution containing the liquid of thv vapour to be measured 
 can be used in the bulbs provided there is sufficient of this liquid to 
 give a pressure greater than the pressure in the gas. A solution will offer 
 advantages over the pure liquid if less total pressure is developed from 
 it, so that the danger of leakage from the flasks is decreased. Further, if 
 a solution is used which gives partial pressures of two or more separate 
 substances, and if these substances were contained in t!ie original gas 
 as vapours, then ihe differential pressure developed between the two 
 flasks will be equai to the sum of the original partial pressures of these 
 vapours in the gas. 
 
 5. The partial pressure of any particular vapour in a sample 
 of gas is independent of the temperature of the gas, provided that 
 the total pressure on the gas remains constant while the volume can 
 change with the temperature, and provided the vapour remains always 
 unsaturated and obeys the simple gas laws. An apparatus con- 
 structed on this principle will, therefore, measure a definite quantity: 
 viz., the pressure of the vapour in a gas at atmospheric pressure. This 
 measurement can easily be reduced to standard pressure. 
 
 6. Though the partial pressure of a vapour i? independent of 
 the temperature, the actual weight of the vapour contained in unit 
 volume of the gas depends on the temperature. For one vapour, this 
 weight may be calculated from the partial pressure, on the assumption 
 that the vapour gives the same partial pressure as it would if it were a 
 true gas at that temperature and molecular concentration. In the case 
 of two or more vapours, the actual weight of each vapour cannot be to 
 calculated, unless the relative proportions of the vapours are also 
 known. This, however, does not impair the usefulness of the method 
 for comparative tests on the total quantities of several vapours, e.g. 
 light oils, in different samples of gas. 
 
 EXPERIMENTAL P.\RT. 
 
 The apparatus used is of the form shown in Fig. 2. Details of 
 the apparatus can be obtained by reference to Paper No. 2 listed on 
 page 15. 
 
 The essential features are : — 
 
 1. Two compensating flasks connected by a manometer. 
 
 2. That these flasks be air tight, but that they can be opened to 
 atmospheric pressure. 
 
 11 
 
, Tha, .hen .h. «ask, .,. clo»d the bulb o. liquid (or »lid) 
 kiS »Wle the manon-eter remams outside. 
 
 W X"a* *: 'b* Mel with the desired liquid (or solid,. 
 b Estate the flask w|i* '^ J,lS.: as'the'"op.?S; 
 \jeHe^tcr.X^ra„fo\a'.Ser"prr^^^^ 
 
 cock* We have found -"f 8« J;\<'„';X°"g^s sampto- The 
 
 '-sti'pte?f™rfr;t"f:^^fusb^^ 
 
 klS;:.?hVlStirs°i'n waStui« Si'lorsutal, samples o, 
 gas. j2 
 
the stop-cock in the manometer, equalize ^ i* j 
 ^^ferte^rSly^ron-r^ie .a, .ide 6r.t. a. 
 the pressure wiU develop the Other >«ay. 5 ^.^ ^nd 
 
 drawing warm air through each side^ ^^^^ ^^H^^ ,^hi h 
 
 Considerable care must be ^a* ;" ^^ }" "^Jl » laboratory tech- 
 ■must have thin bottoms A person w.th^^^^^^^ .^ ^ ^^ ,i 
 
 ffiis'rtr/'i^-eSSeV^^^^^^^^^^^ -^^^^^"°^ ^^^ '^^^" '" 
 
 ^-^SSe L^JS^in^fs can ^^rn^de ."i. su^^^^^^^^^ a room 
 
 required. efficiency of the method. 
 
 in order to check the -^"^ J^^ netlir w^^^^^^^^ 
 which different known Quantities of benzene in ^^^^^ ^j ^^^ 
 
 S:.r^d SurS^vatef r7hir£n\Vi-n^s being within 
 
 '■' ^W^hen, however the air contained to^^^^^^^^ 
 the benzene, it was fo""^ that the toUiene p y ^^^ ^.(^^,^^^,^1 
 liquid benzene in the bottoni of the HasK. ^ ^ ^^ pressure of 
 
 p?essure recorded was not the Pr^««^^^«^°^ Sved out. If sufficient 
 Lnzene plus the pressure «/ /^l^X^n" jS out, and thediflfer- 
 S Xure^n rrp'retfe rh^^m^of the benzene and toluene 
 pressures in the original samp e ^l a.r^ following liquids 
 
 „ Jir.r='absra^"r«S ?,SXon.e„t o. mu^.a.ng .as, 
 
 In the first case, the toluene^and xyk^ tr^^^^^^ ^^^ ^^1^^„^ 
 
 the benzene. In the ^°"^ ca«.. the pr^^^^^^^^^ 
 Sh^gTrndXt'^rriSate^^^ P-iple. In the third 
 
 Ssealfthree vapours are estimated in this way. 
 
 THK ESTIMATION OF THE BENZENE CONTENT OF COAL 0A8. 
 
 It has already been pointed -^J^^^^^^^frDi^l^^^^^^^ 
 
 SS'MX^ilSS^^-^^ I^nzene 
 
 1. The toluene and "ther light oils ms^ . ^^^^ ^j^^ ^^^^ 
 
 so that their pressures are almost entirely rem 
 
 13 
 
while, at the same time, these dissolved substances lower the vapour 
 pressure of the benzene. .... 
 
 2. A less serious error is caused by the gases other than the hght 
 oils dissolving in the liquid benzene. 
 
 In order to eliminate these sources of error, we have conducted 
 investigations on gases by the Differential Pressure Method, using 
 bulbs filled with solid benzene, and immersing the apparatus in a bath 
 below the freezing point of benzene, S • 48°. It is well known that the 
 solubility of permanent gases in a solid, such as frozen benzene, is 
 vanishingly small, so that the second source of error mentioned above 
 is c( mpletely removed. . 
 
 Again, the vapour pressure from the solid benzene is, at any hxed 
 temperature, independent of the solution by which it is surrounded, 
 so that while the solid benzene is present at equilibrium there can be 
 no lowering of the vapour pressure. , . , - . ... 
 
 The experiments were highly successful. It was found possible 
 to determine the benzene content of a gas in this manner with con- 
 siderable accuracy, even when fairly large quantities of toluene and 
 xylene were present in the gas. 
 
 It is quite easy to keep a bath for the apparatus at a temperature 
 near 0° with ice and water. The chief difficulty we experienced was in 
 freezing the small bulbs of benzene, for they could be enormously 
 supercooled. The best method is to freeze them in the escaping 
 stre.ir of liquid and gas from a carbon dioxide cylinder. Once 
 frozen, they are of course quite stable for several degrees above zero. 
 
 As far as we know this is the only method by which the benzene 
 content only can be found accurately in a small sample of gas which 
 contains also its homologues. 
 
 CONTENTS OF THE RICH AND POOR WASHING OILS. 
 
 In order to measure the vapour pressures of the light oils from the 
 rich and poor washing oils, we have used two methods: — 
 
 1. A small amount of air was shaken up with a large amount of 
 washing oil until equilbrium was reached. The quantity of oil must 
 be so large that its concentration of light oils is not appreciably 
 affected by the amount which evapor tes into the air. The air was 
 then drawn into a Differential Pressure Apparatus and analysed for 
 its total light-oil content. . ..... j u iu 
 
 2. About 5 gm. of the oil was sealed up in a thin-bottomed bulb. 
 The bulb was then placed in a Differential Pressure Apparatus whose 
 flasks had a small capacity. After equilibrium was reached, the bulb 
 was broken and the pressure of light oils from the washing oil measured 
 
 By means of these measurements, and those previously described 
 in this paper, a close check can be kept on the efficiency of the washing 
 system, and on the steam distillation stills of a light-oil recovery plant, 
 and this in general will lead to an increased production. 
 
 IV. CONCLUSION. 
 
 It is possible that the methods outlined in this paper may be of 
 use in other fields besides light-oil recovery. In natural processes and 
 
 14 
 
in many industries it often happens that large quantities of gas 
 mixtures are produced which contain the vapours of valuable liquids. 
 Thus, natural gas often contains, as vapours, quantities of the sub- 
 stances which constitute gasolene, while methyl alcohol and acetone 
 vapours exist in the gases given ofT during the destructive distillation of 
 wood. The method may also prove useful for the quick estimation of 
 the water content of air. 
 
 Finally, it is hoped that by this method of analysis it will be 
 possible to obtain more precise knowledge concerning the effect of 
 conditions of coking on the production of Hght oils. We have done 
 some preliminary work on the variation of the light-oil content in 
 illuminating gas with the different stages of coking, but extensive 
 research with good equipment is needed in this field from which so 
 much information of great economic value is still to be obtained. 
 
 V. PREVIOUS PUBLICATIONS ON THE SUBJECT BY THE 
 
 AUTHORS. 
 
 1 . The Extraction of Aromatic Hydrocarbons from Gases by means 
 
 of Liquid Absorbents, by Harold S. Davis. University of Mani- 
 toba publications, 1917. 
 
 2 . A new Method for the Estimation of Vapours in Gases, by Harold 
 
 S. Davis and Mary Davidson Davis. J. Ind. and Eng. Chem. 
 (In Press). 
 
 3. The Application of the Differential Pressure Method to the 
 
 Estimation of the Benzene and of the total Light Oil Content 
 of Gases, by Harold S. Davis, Mary D. Davis and Donald G. 
 MacGregor. J. Ind. and Ei.g. Chem. (In Press). 
 
 4. Studies on the Absorption of Light Oils from Gases, by Harold S. 
 
 Davis and Mary D. Davis. J. Ind. and Eng. Chem. (In Press). 
 
 5. "A Process for the Quantitative Estimation of Vapours in Gases." 
 
 U.S.A. Patent No. 1,272,922, July 16,1918. 
 
 Clifton, Colchester Co., 
 Nova Scotia. 
 
 15 
 
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