Determination of Gossypol in Crude Cottonseed Oil H. D. ROYCE, J. R. HARRISON, AND PARKER D. DEANS The Southern Cotton Oil Company, Savannah, Ga.
S
MITH and Halverson (5) recently pointed out a possible
source of error in the pyridine-aniline method for the determination of gossypol, due to the presence of pyridine of crystallization in the precipitate of dianilinogossypol. With reference to the original paper ( 2 ) on the method, this criticism probably is justified, since the proposed procedure of drying the precipitate (1 hour's heating at 100" C.) did not assure quantitative removal of the pyridine. However, a modification (3) published the following year, provided for heating the dianilinogossypol to constant weight at 100" C., and the present paper demonstrates that the pyridine of crystallization retained by the precipitate can be removed quantitatively, without appreciable decomposition of the dianilinogossypol. Jl'hile this removal may be accomplished at 100" C., i t can be effected more rapidly and conveniently at a higher temperature. Also, the dianilinogossypol precipitated with 2 molecules of pyridine of crystallization can be dried to constant weight a t a low temperature, without loss of pyridine, so that the dianilinogossypol-dipyridinemay be weighed as such and calculated to gossypol by means of the conversion factor 0.627. I n the course of this work another minor modification of the original method was found to give increased accuracy and reliability. The addition of a small amount of pyridine to the petroleum ether used for washing the dianilinogossypoldipyridine reduced the solubility of the precipitate to an appreciable extent, making it possible to recover up to 98 per cent of the gossypol from a 0.2 per cent solution in oil. These improvements are embodied in a revision of the method presented herein, and the experimental data forming the bases for these changes are summarized. I n a recent paper, Campbell, Morris, and Adams ( 1 ) described the preparation of a dipyridine salt of gossypol, C30H300s.2CbH~K. On account of the possible interference of such a compound in the determination of gossypol by the pyridine-aniline method, a few notes on the precipitation of gossypol from pyridine solutions, in the absence of aniline, are included in the present paper. I n general, pyridine alone would not precipitate gossypol from crude cottonseed oil, and the solubility of the pyridine salt was sufficient to preclude contamination of the dianilinogossypol-pyridine complex. The solubility of gossypol in pyridine was found to be 13.3 per cent by weight, and upon dilution of this saturated solution with petroleum ether, a crystalline precipitate of 2C3"HsoOs.5CjHjNJ rather than the dipyridine salt, was obtained.
moval of the solvent under reduced pressure. The gossypol concentration was adjusted to 0.4 per cent, so that the 25-gram samples taken for analysis contained exactly 100.0 mg. of gossypol. The gossypol had been purified by recrystallization from a petroleum ether-ether mixture, and was a bright yellow, microcrystalline powder having a molecular weight of 518 (titration with 0.25 N sodium hydroxide), and melting point of 184' C. A further indication of the purity of this preparation is the crystal form, shown in Figure 1. The pyridine and aniline employed in this work were c. P. grade (Baker), and the petroleum ether was Skellysolve F (boiling range 35" to SO'). With the exception of heating conditions and details outlined in Table I, the general analytical procedure was that described in a previous paper (3). Unless otherwise stated, all the gossypol analyses given in the tables are averages of three determinations. Samples 1 to 3, Table I, show that the dianilinogossypolpyridine complex reaches constant weight in 2 hours at 60" C., and that the nitrogen content remains fairly constant. The pyridine content of the precipitate was calculated from the nitrogen analysis, by means of the following equation: 17.72 P or
+ 4.19(100 - P ) = 100 N P = 7.41 N
- 30.9
where P = per cent pyridine, N = per cent nitrogen, and 17.72 and 4.19 represent the nitrogen percentages in pyridine and dianilinogossypol, respectively.
Experimental EFFECT OF HEATING COXDITIOSS ON COMPOSITION OF DIANILINOGOSSYPOL PRECIPITATED FROM COTTONSEED OIL WITH A MIXTUREOF PYRIDINE AND ANILINE.-A stock solution of purified gossypol in refined cottonseed oil was prepared by adding an ethereal solution of gossypol to the oil, followed by complete re-
FIGURE 1. PURIFIED GOSSYPOL X 450. m. p. 184' C., crystallized from a mixture of ether and petroleum ether
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INDUSTRIAL AND EKGINEERING CHEMISTRY
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Samples 4 to 8, Table I, show that when the dianilinogossypol-dipyridine is held tonseed oil; 7.5 ml. of pyridine-aniline reagent (4 t o 1).a n d 50 ml. of petroleum ether added, allowed t o precipitate at 100" C., the pyridine is 7 days a t room temperature. Samples 12 t o 15, inclusive, represent 100-gram samples of typical hot-pressed crude cottonseed oil, no added gossypol.) driven off slo\dy but cluanG O S.. WDO Found ~ titatively, constant weight Precipitate weighed as Pyridine Corrected for being attained in about 9 Heating Conditions Weight Content analyzed CI~HI~S~OLhours, and the nitrogen conTemof PreNitrogen Calcd. from pyridine 2CbHsK Sample perature Time cipitate Content Nitrogen content (factor 0.627) tent (4.12 per cent) indicates C. Hours Mg. % % MQ. MQ. that all the pyridine has 1 60 1 157.0 6.60 18.0 99.9 98.4 2 been expelled, without de2 155.0 6.56 17.7 99.1 97.1 3 3 155.0 6.54 17.6 99.4 97.1 composition of the residual 100 3 134.9 4.79 4.4 99.9 ... dianilinogossypol. I n all 5 128.3 4.48 2.2 97.3 ... 7 126.8 4.30 0.8 97.5 ... cases (samples 7 to 11, in9 124.8 4.11 None 96.7 ... 12 124.5 4.12 None 96.5 ... clusive) where the nitrogen 9 160 0.5 125.3 4.11 None 96.9 content of the precipitate is 10 1 124.6 4.08 None 96.6 equal to or less than that 11 2 125.0 4.06 Sone 96.6 of pure dianilinogossypol 12 C r u d e cottonseed oil 117 60 2 197.6 6.73 19.0 124.1 123.8 (4.19 per cent), the absence 13 Crude cottonseed oil 117 160 1 158.7 4.29 None 123.0 ... of pyridine is assumed, and 1 4 C r u d e cotton9 the weight of precipitate is seed oil 300 60 174.4 6.62 18.2 110.4 109.3 15 C r u d e cottonconverted to gossypol by 1 seed oil 300 160 MG.4 4.07 h-one 113.5 ... means of the factnr 0.773. Employing a drying temperature of 160" C., conTABLE11. EFFECTOF WASHIKGPROCEDURE IS PYRIDISE-ANILINE METHOD stant weight is obtained in 30 (Each sample contained 100.0 mg. of gossypol i n 49.90 grams of cottonseed oil; 70 ml. of Skellysolve F, 6 mi. of pyridine. a n d 1.5 mi. of aniline were added, mixed, and allowed t o s t a n d 5 days.) to 60 minutes, and the nitroComposition of Wash Solution gen content bf the residue Skellysolve F Skellysolve F Containing 2% Pj-ridine Experiment Volume W t . of Nitrogenb GossypolC Ifr:. of Kitrogen Gossypol (sample 10, 4.08 per cent) NO. of Wash precipitaten content found precipitate content found indicates that i t is free from M Q. Ml. Itfg . % MQ. MQ. % pyridine. Further evidence 1 GO 120.6 93.5 127.0 4.09 98.4 2 120 119.8 4:&3 92.8 126.2 4.07 97.7 that the residue is tliani3 180 117.2 4.04 90.8 124.0 4.22 '36.1 linogossypol is shown by the 4 240 108.8 .. 84.3 123.6 4.12 95.8 Calculated values for percentage recovery (96.6), 1 0 0 ~ orecovery 129,o 4.19 100.0 129.0 4.19 100.0 since this figure was oba All precipitates heated one hour a t 160' C., a n d weighed as dianilinogossypol. tained by using the dianib Nitrogen values are given t o show complete removal of pyridine from dianilinogossypol-dipyridine by heating 1 hour a t 160' C. Weight of precipitate multiplied b y factor 0.775. 1i n o g o s s y p o 1 c o 11version factor (0.775), antl is in agreement with the normal perc e n t a g e r e c o v e r y usually The gossypol content of the precipitate is then calculated by attainable from a dilute solution of gossypol in oil. subtracting the weight of pyridine from the weight of precipiOn the basis of these experiments, it is reconimended that a tate, and multiplying the difference by the dianilinogossypol 1-hour heat at160" C. be substituted for the former procedure factor (0.775). The analyzed pyridine content of the precipiof heating the precipitate to constant weight a t 100" C. This tate, heated to constant weight a t 60" C., is slightly lower than change minimizes the danger of pyridine retention and shortthe calculated value (19.2 per cent) for C~~HJ206.2CsH,S, ens the time required for analysis. but it is probable that the discrepancy is due to low nitrogen An alternative procedure for handling the precipitate is to values returned by the Kjeldahl method on samples containheat 2 hours a t 60" C., leaving a residue of dianilinogossypol ing pyridine compounds. Three samples of purified, anhycontaining 2 molecules of pyridine, in which case the converdrous pyridine, analyzed by the Kjeldahl method, gave 17.39, sion factor is 0.627. However, owing to the possibility of in17.29, and 17.69 per cent of nit'rogen, respectively, for an complete removal of moisture and solvent a t 60" C.?it is average of 17.46 per cent, which is 0.27 per cent lower than the usually preferable to drive off the pyridine of crystallization a t calculated value of 1T.72 per cent. 160" C. anti Tveigh as dianilinogossypol. As further evidence that the dianilinogossypol-pyridine Samples 12 to 15, inclusive, Table I, indicate that the precomplex, upon heating to constant weight at 60" C., contains cipitate of dianilinogossypol-dipyridineobtained from crude the theoretical percentage (19.2) of pyridine for the dipyridine hot-pressed cottonseed oil may be treated as above, and either salt, i t will be noted in Table I that the calculated gossypol weighed as the dipyritline salt (factor 0.627), or heated to recovery, based on the analyzed pyridine content, is too high 160" C. and \yeighed as dianilinogossypol (factor 0.775). (99.1 to 99.9 per cent recovery). Owing to the appreciable Khile one of the samples heated to 160" C. ( S o . 13) shows solubility of the dianilinogossypol in the mixture of oil, petroa nitrogen content ?lightly higher than the calculated value for leum ether, pyridine, and aniline from n-hich it precipitates, dianilinogossypol (4.19 per cent), no residual pyridine could the actual recovery cannot greatly exceed 98 per cent. be detected in the precipitate and, when calculated to gossyIf, instead of using the analyzed pyridine percentage for pol by means of the factor 0.775, fair agreement with the recorrection, the theoretical value (19.2 per cent) for sults based on weighing the dipyridine salt were obtained. CazH4,N1O6.2CsH59 be used, t'he amount of gossypol found is The precipitates formed in crude cottonseed oils with the about what would be expected-for example, on sample 2 , pyridine-aniline reagent are invariably macrocrystalline, and assuming the theoretical pyridine cont'ent of 19.2 per cent, the while not so coarse and brightly colored as those formed in the factor for converting the dianilinogossypol-dipyridinesalt to stock solution of purified gossypol in refined oil, they are easy gossypol is 0.627, and the gossypol recovery is 97.1 mg. to wash antl filter. CONDITIOXS ON PYRIDINE CONTENT OF PRECIPITATE TABLEI. EFFECTOF HEATING (Samples,l t o 11, inclusive, contain 100.0 mg. of pure gossypol (molecular weight 518) in 24.90 grams of refined cot-
O
7
C
~
~~
ANALYTICAL EDITION
DECEMBER 15. 1940 TABLE
111. RATEOF
PRECIPIT.4TION O F
COTTONSEED OIL
GOSSYPOL FROM
(Samples contain 100.0 mg. of gossypol dissolved i n 49.9 grams of refined cottonseed oil, 7 0 ml. of petroleum ether) Gossypol CrystalWeight Recovered (100.0 Rlg. lization of PrePreciuitatina Agent Time cipitatea Present) Samule 20
6 ml. of pyridine
24 25 26
DOUS
Mu.
Mg.
14
S o ppt.
Kone
4
122.4 123.4 125.0
5 7 14 1 2
27
125.2 46.6
4
48.0 60.2 67.0
5
80.0
3
7
36.1 37.2 46.6 51.9 62.0
96.0 74.4 103.0 79.8 H e a t e d 1 hour a t 160° C., converted to gossypol by factor 0.775. 14
a
Modified Washing Procedure The advantages of adding a small amount of pyridine to the
143
20, Table 111. Since the formatiori of an insoluble pyridine salt of gossypol has been reported in the literature (I), the solubility of gossypol in pyridine was studied further. I n the first experiment, the work referred to above was repeated. One hundred milligrams of pure gossypol were dissolved in 10 ml. of c. P. pyridine, and the solution was diluted with several volumes of petroleum ether. No precipitate formed on standing 14 days. The solubility of gossypol in pyridine was then determined, and found to be 13.3 per cent by weight, at 25' C. Upon dilution of this saturated solution with petroleuni ether, a finely crystalline, greenish-yellow precipitate formed, rvhich, upon heating 42 hours at 60" C., analyzed 5.18 per cent nitrogen. The precipitate mas still losing n-eight, though very slowly, at the end of the heating period, 2.095 grams losing 2.4 ~ n g in . the last 3 hours. The nitrogen content of 5.18 per cent is equal to 29.2 per cent pyridine, or a ratio of 2.5 moles of pyridine per mole of gossypol, corresponding to the fomiula 2(:30H3n0s.5CjH~N. This substance was then heated at 100' C , until it approached constant weight (3 hours), whereupon reduced to 0.95 per cent, equivalent to slightly less than 0.5 mole per mole o C3nH3008.1/2CjH6N, 1.03 per cent of nitrogen). In view of the fact that the precipitate was still losing weight slowly when the nitrogen analysis \yas made, proof of the existence of the compound C3~H3nO~.1/2C~H& is not claimed. Upon heating at higher temperatures, the gossypol darkened and decomposed while liberating the remainder of the pyridine.
petroleum ether used in washing the precipitated dianilinogossypol-pyridine complex are shown by Table 11. An excessive amount of washing lowers the recovery, particularly when From the above observations it is apparent that the coinno pyridine is added to the wash. Depending upon the washparatively high solubility of gossypol in pyridine precludes ing technique, the minimum volume of petroleum ether the interference of pyridine-gossypol salts in the precipitation necessary t'o ensure complete transference of the precipitate of the dianilinogossypol-pyridine complex from cottonseed oil from flask to filter, and complete removal of oil, will vary with a mixture of pyridine and aniline. somewhat, but usually a t least 50 ml. are required, and a wash Another factor which affects the precipitation of gossypol volume of 60 ml. is recommended as a standard procedure. from a dilute oil solution is solvent volume. Table IV shows h'itrogen deterniinat'ions were made on the washed precipithat while this volume is not very critical, complete precipitatates to check on the possibility of error due to pyridine tion cannot be obt'ained in the absence of petroleum ether, nor retention by the samples washed with the pyridine solution. can maximum recovery be obtained when the solvent volume However, after heating the samples 1 hour a t 160" C., those is more than twice the sample volume. The solvent also washed with the pyridine solution have about the same nitroserves the purpose of speeding u p the filtration. gen content as those washed n-ith petroleum ether, so that no Inasmuch as many types of crude hot-pressed Cottonseed error is introduced by weighing as dianilinogossypol and conoils contain appreciable amounts of nonfats which are insoluverting to gossypol by the factor 0.775. The pyridine wash ble in petroleum ether, it was thought advisable to check the makes possible a recovery of 98.1 mg. of gossypol from a solution contailling 100 mg. in 50 grams of oil, whereas the old method recovers only 93.5 mg. from the same solution. O F SOLVENT VOLUVE ON PRECIPITATION O F TABLE Iv. EFFECT The effect of pyridine on the rate and completeness of GOSSYPOL FROM CRUDE COTTONSEED O I L precipitation of dianilinogossypol from oil solution is well (50 grams of oil, 6 ml. of pyridine, 1.5 ml. of aniline, diluted with specified illustrated by the tests in Table 111 (samples 20 to 34). All amounts of petroleum ether, allowed t o precipitate 7 d a y s ) the analyses in these tests were run under identical condiPetroleum E t h e r Sample (Skellysolve F) Gossypol Found tions, except for t'he omission of pyridine in the second series, M1. % so that the results are directly comparable. I n the absence 0.055 None 60 of pyridine, precipitation is relatively slow and incomplete, 0.098 35 62 0.096 64 amounting to only " 80 Der . cent recoreryin 14 days (sample 34). 0.093 1 :; 66 68 140 0.074 With pyridine present, more than 80 per cent of the gossypol is precipitated the first day, OF WASHING PROCEDURES o s PYRIDISE S ~ LOF T DIANILINOGOSSYPOL T ~ B LV.E EFFECT and the reaction is virtually PRECIPITATED FROM CRUDE C O T T O S s E E D O I L complete in 7 days. giving a reWeight of ,Precipitate Dried t o covery of 96.9 per cent. ExConstant Weight Gosaypol tending the precipitation period Washin:: Procedurea a t 160' C. Found Sample t o 14 days only increases the Gram % 5 ml. of 95% alcohol, followed b y 10 90 Crude cottonseed oil No. 3 (50.0 grams) percentage recovery to 97.0, so ml. of 50% alcohol and 10 nil. of water 0,0809 0 125 that for all practical purposes a 91 Crude cottonseed oil S o . 3 (50.0 grams) Three 10-ml. portions of hot 50% alcohol 0.0815 0.126 7-day precipitation period is 92 Crude cottonseed oil S o . 3 (50.0 grams) Three 10-ml. portions of hot water folsufficient, in the presence of lowed by 5 ml., of 95% alcohol 0.0823 0.12s 93 Crude cottonseed oil S o . 3 (50.0 grams) T w o 10-ml. p o r t ~ o n sof hot 50% pyripyridine. 0,0836 0.130 dine
-
Pyridine Salts of Gossypol Pyridine alone does not precipitate gossypol from dilute oil solutions, as shown by sample
94
Crude cottonseed oil S o . 3 (50.0 grams)
95
Crude coltonseed oil S o . 3 (50.0 grams)
96 97
011S O .
Oil No. 3 plus 100 mg. of gossypol 3: plus 100 mg. of gossypol
10 ml. of hot 50% psridine, 10 mi. of water 10 ml. of 95% alcohol T w o 1O~ml.portions equal parts pyridine a n d alcohol Same as i n 94 Same as i n 93
0.0819
0.127
0.0854 0.2220 0.2210
0.132 0.344 0.342
Initial wash with 60 ml. of Skellysolve F containing 2 per cent pyridine preceded above washes in every ca8e.
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presence of such compounds in the dianilinogossypol-dipyridine complex by washing with water, aqueous solutions of alcohol, and pyridine. Moreover, Smith in his revised method for the determination of gossypol in cottonseed meal (4) specifies a n alcohol and water wash, and owing to the chance of water-soluble meal extractives being present in crude oil, a similar washing treatment was tested in the present method. However, reference to Table V indicates that neither water, alcohol, nor pyridine washes change the weight of the precipitate to any significant degree. The effect of adding purified gossypol to a crude oil prior to analysis is shown by samples 96 and 97, to which 0.2 per cent of gossypol was added. Taking 0.128 per cent as the average amount of gossypol found in the crude oil, samples 96 and 97 would be expected to return 0.328 per cent, whereas the actual recovery was 0.343 per cent. This increase in recovery may be explained b y the seeding action of the added gossypol, whereby precipitation of dianilinogossypol is brought about soon after addition of the reagents, and a large number of crystal nuclei are formed to act as centers of subsequent crystal growth. I n the absence of this added gossypol, precipitation does not start for several days after the addition of the pyridine-aniline, and even after the first appearance of the precipitate, crystal nuclei are not numerous enough to bring the precipitation to completion in 7 days. Precipitation is hastened by agitating the samples for a brief period each day after the initial appearance of crystals. On the basis of the results of the foregoing experiments, the following revision of the pyridine-aniline method for the determination of gossypol in crude cottonseed oil is outlined.
The above method will recover 95 to 98 per cent of the gossypol from a 0.1 per cent oil solution, which is about the average gossypol concentration encountered in analysis of hotpressed cottonseed oils. The reproducibility of results is fairly good for this type of analysis, as shown by the results obtained on two commercial samples of hot-pressed oil, an expeller oil, and a stock solution of 0.1 per cent gossypol in refined cottonseed oil (Table VI). Referring to sample 1, it mill be noted that the results are not closely reproducible on oils containing less than 0.01 per cent of gossypol, because precipitation is relatively blow and incomplete. At 0.1 per cent and higher concentrations the method is satisfactory. Sample 4 indicates that better checks can be obtained on stock solutions of purified gossypol in refined oil than on corresponding concentrations of gossypol in crude oil (sample a ) , probably because of the presence of gossypol degradation products and other nonfats in the crude oil. As recommended in an earlier paper ( 2 ) accuracy and reproducibility of results on oil samples containing less than 0.01 per cent of gossypol are improved b y the addition of a known amount of pure gossypol to the oil being analyzed.
Proposed LVodificationof Pyridine-Aniline lMethod
Literature Cited
Summary
A mixture of pyridine and aniline is more effective than aniline alone in precipitating gossypol from crude cottonseed oil. A modification of the pyridine-aniline method, which recovers up to 98 per cent of gossypol from a 0.2 per cent solution in oil, is described. The pyridine-aniline reagent precipitates dianilinogossypol containing 2 molecules of pyridine of crystallization. The pyridine is removed quantitatively, without decomposition of the residual dianilinogossypol, by heating the precipitate 1 OF DETERMINATIONS AT VARIOUS TABLE VI. REPRODUCIBILITY hour a t 160 O C. The dianilinogossypol-dipyridinecomplex GOSSYPOL CONCENTRATIONS is fairly stable at 60" C., and after heating for 2 hours a t this Percentage temperature, its composition corresponds closely to the forGossypol Deviation from M e a n Found Mean Sample mula C42H40N206.2C6H6X. % % The addition of a small amount of pyridine to the petroleum 0.0036 0.0039 7.7 1 Hot-pressed oil A ether used for washing the dianilinogossypol precipitate de0.0042 creases the solubility of the precipitate, and gives higher re2 Hot-pressed oil B 0.110 0.1115 1.4 0.113 covery of gossypol from dilute oil solutions. 3 Expeller oil E 1.370 1.386 1.1 Pyridine alone will not precipitate gossypol from crude 1.402 cottonseed oil. The solubility of gossypol in pyridine was 4 Stock solution of, 0.1% gossypol in cottonseed oil 0.095 0.0955 0.5 found to be 13.3 per cent by weight a t 25' C. A pyridine0.096 is gossypol complex having the formula 2C30H~008.5C5H6N described.
Weigh 50 grams of filtered crude cottonseed oil in a 200-ml. wide-mouthed extraction flask and dilute to 110 to 130 ml. with petroleum ether (Skellysolve F). Add 10 ml. of a mixture of 4 parts pyridine and 1 part aniline, mix well by swirling, stopper loosely, and store in a warm place (35' to 40" C.) for several hours. Replace any solvent lost by evaporation, and hold the samples at room temperature for 7 to 14 days. To prevent undue loss of solvent during the precipitation period, tight-fitting stoppers provided with a capillary vent may be employed. In any case maintain the solvent volume close to its original value throughout the precipitationand agitate the samples once each day after precipitation has begun. Oils containing less than 0.1 per cent of gossypol should be allowed 14 days to precipitate. Filter under suction on tared crucibles provided with medium asbestos mat, washing the crystals of dianilinogossypol-dipyridine onto the filter with petroleum ether containing 1 to 3 per cent of pyridine. Wash the crystals free from oil with this solvent mixture, keeping the total volume of wash below 100 ml. Drive off the pyridine of crystallization by heating the precipitate 1 hour a t 160" C., and weigh as dianilinogossypol. If it is desired to weigh the precipitate as dianilinogossypol-dipyridine, heat 2 hours at 60" C. The factors for converting weights of dianilinogossypol and dianilinogossypol-dipyridine to gossypol are 0.775 and 0.627, respectively.
(1) Campbell, Morris, and Adarns, J . Am. Chem. Soc., 59, 1723 (1937). (2) Royce, Oil & Soap, 10, 183 (1933). (3) Royce and Kibler, Ibid., 11, 116 (1934). (4) Smith, F. H., IND. EVG.CHEX, Anal. Ed., 9, 517 (1937). (5) Smith and Halverson, Ibid., 11, 476 (1939).
Jacketed Receiver for Vacuum Distillation Our attention has been called by Baird and Tatlock (London),
Ltd., to the similarity between the jacketed receiver for vacuum distillation described by J. B. Cloke [IND.ESG. CHEY.,Anal. Ed., 12, 329 (1940)], and a receiver designed by Dr. Linnell of the Pharmaceutical Society of Great Britain. The Linnell type, described in a bulletin of the manufacturer, differs mainly from that suggested by Cloke in that it is not graduated, has no "dripper", has a simplified stopcock arrangement, and has proportionately more condenser surface between the side entry and the vacuum connection. The receiver is a modification of the Perkin vacuum triangle. Both receivers may be used advantageously with the new jacketed Pyrex flasks made by the Corning Glass Co.
