June,
T H E J O C R N A L O F I N D U S T R I A L A N D EATGINEERIil‘G C H E M I S T R Y
191j
which he addressed t o t h e Academy of Medicine a n d Sciences. “I-Complete i m m u n i t y from cholera of t h e immense majority of all workmen whose calling necessit a t e s their being habitually in contact with copper dust. “a-Copper a n d its alloys, brass a n d bronze, permanently applied t o large surfaces of t h e common integument, are a most precious preventative, which ought in no mise t o be neglected a n d can cause no inconvenience. If these means leave something t o be desired as a prophylactic, it will probably be found expedient t o reduce t h e metal t o a n impalpable powder a n d t o ingest a few pinches. ‘:3-111 t h e t r e a t m e n t of cholera, copper, opportunely administered, whether in copper filing alone or in a n y other form which experience shall determine, affords t h e greatest probability of proving in t h e hands of t h e physician a powerful means of cure.” Having been convinced t h a t even in fairly large doses copper sulfate is harmless t o t h e h u m a n system, I tried its germicidal effect in t h e Taylor Gymnasium pool. Xs. t h e pool water a t t h e time was being refiltered daily, a small amount of alum being added t o aid t h e mechanical filter-I took t h e opportunity of first determining t h e efficiency of t h e alum t r e a t ment. A s t h e copper t r e a t m e n t immediately followed t h e alum t r e a t m e n t , I have tabulated m y results together. Table I11 shows t h e results of t h e use of alum a n d of alum a n d copper sulfate.
499
S L-1111.4 R Y
The advantages of copper sulfate over hypochlorite of lime as a disinfectant for swimming pools therefore may be summarized as follows: I-It is more effective because i t does not undergo chemical change readily. Hypochlorite owes its power t o t h e chemical change a n d is afterwards useless. 11-It is not irritating t o t h e eyes a n d mucous membranes as is iihypochlorite” if t h e latter is used in germicidal quantities. 111-It is cheaper. IT‘-It has no odor. If all other conditions were equal this last fact alone would prove its great advantage over “hypochlorite.” DEPARTMENT O F BIOLOGY,LEHICHUNIVERSITY SOUTH BETHLEHEM, PA
THE VALUATION OF COMMERCIAL ARSENATE OF LEAD By R . H. ROBINSON AND H. V. TARTAR Received January 16, 1915
T h e practical value of t h e arsenates of lead as insecticides depends upon their arsenic content a n d their comparative insolubility in water which prevents t h e m from being injurious t o foliage. There are three arsenates known: t h e lead of hydrogen or “ a c i d ” arsenate, t h e basic or “ n e u t r a l ” arsenate, a n d t h e pyroarsenate. T h e latter salt is unimportant from a spray standpoint, since it is probably not present in t h e commepcial brands upon t h e market, due t o t h e fact t h a t t h e pyro salt cannot exist in t h e presence of water a n d , t h u s far, has been prepared only b y heating t h e pure hydrogen arsenate a t high temperatures as shown by T a r t a r a n d Robinson.’ Previous investigaT s a i E 111-BACTERIOLOGICALEXAMINATION O F TAYLOR GYMNASICM tions by T a r t a r a n d Robinson’ have shown t h a t pure SWIMXING P O O L Gelatin B. coli Gelatin B . coli lead hydrogen arsenate can be prepared corresponding Date count per D a t e count per 1914 per cc. cc. ADDITIONS 1914 per cc. cc. ADDITIONS in composition t o t h e theoretical formula PbHAs04, 5/20 8 , 0 0 0 1 , 0 0 0 ) 5/11 4 0 giving upon analysis 32.98 per cent arsenic oxide a n d 21 6 , 0 0 0 50 1.0 p. p. m. 11 790 7 22 1 8 , 0 0 0 100) alum per day 63.92 per cent lead oxide. The basic arsenate was 1 2 9 , 0 0 0 180) 23 30,000 150 13 18,000 100 24 9 , 0 0 0 80 also found t o be of constant composition when pre14 48,000 90 ’.’ P . P. m. 25 27,000 300 1 5 16,500 2 5 0 per 26 5 , 0 0 0 pared from pure salts a n d gave upon analysis 23.42 2i 2,500 ;) 16 6 , 9 0 0 400 28 100 0 0.04 p. p , m. 1 i 36,000 400’ per cent arsenic oxide a n d 7 4 . 7 2 per cent lead oxide. 29 2 , 0 0 0 CU,U~SO~ per Practically, t h e n , there are two kinds of lead ar18 4 , 8 0 0 20 22,000 gallons 30 500 fresh water 6/ 2 5 , 0 0 0 9 senates: ( I ) the hydrogen, a n d ( 2 ) t h e basic arsenate 19 10,000 200 3 6,000 14 generally used as a spray material; manufacturers of Gelatin count B. coli AVERAGE P E R \TrEEK per cc. per cc. commercial brands usually produce one or t h e other 1st Alum t r e a t m e n t . , . . . . . . . , . . . . . , . . . . 35,000 390 form a n d label t h e m as such. T h e hydrogen arsenate 1,500 148 2nd 2.5 p . p. m. “hydrochlorite”. . . . . . . . . . 0.4 p . p. m. CuSOa.. . . , . . , . , . , , , . . . . 3,014 5 3rd is found on t h e market under t h e trades name “ a c i d ” Although copper sulfate is slightly more expensive or “dibasic” arsenate of lead a n d t h e basic is commonly t h a n hypochlorite of lime, a b o u t $1.00 per hundred- known a s t h e “ n e u t r a l , ” “triplumbic” or ‘ I tribasic” weight, i t is effective in much smaller quantities a n d arsenate of lead. There are, however, many brands t h a t do not specify either a hydrogen or a basic sample hence is cheaper t o use. T h e germicidal action of t h e copper sulfate is proba- b u t are simply labeled “arsenate of lead.” I n t h e analysis of t h e commercial brands of lead bly t h a t of a crystalloid, permeating t h e cell wall arsenates, t h e specific determinations usually required, a n d thereby producing t h e toxic effects. as evidence t h a t t h e product is not a violation of t h e I n t h e presence of t h e bicarbonate of magnesium a n d Federal Insecticide Law, consist of a n estimation of calcium t h e following reaction takes place : t o t a l arsenic oxide, total lead oxide, water-soluble CuS04 C a ( H C O y ) r = CaSOa C U ( O H ) ~ 2C02 arsenic oxide, a n d moisture. This is sufficient t o This chemical change, while it destroys t h e toxic ascertain whether t h e sample fulfills t h e requirements power of t h e salt, really aids in t h e ultimate purifica- a s demanded b y law, b u t it does not give evidence of tion of t h e water since t h e hydroxide formed acts a s a t h e exact nature of t h e sample. coagulant uniting with t h e suspended organic matter. 1 T a r t a r a n d Robinson, J . A . C. S., 36 (1914). 1843.
I
+
+
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
500
For t h e t r u e valuation of these commercial samples, therefore, method’s for their complete analysis are necessary. It is not enough t o know t h e total arsenic or lead content t o ascertain t h e value of t h e spray material as a n insecticide, b u t i t is equally important t o understand t h e forms in which these elements are combined, a n d t o what extent t h e y exist as such. For example, if a sample is found t o contain lead combined in t h e form of t h e basic or hydrogen arsenate, t h e carbonate a n d t h e chloride, t h e proportion a n d t h e extent t o which each compound is present is a n import a n t consideration, a n d the estimation of each of these forms is essential in t h e valuation of t h e insecticide. Any other substance or impurity t h a t would also depreciate t h e value of t h e sample is a factor in its valuation. These impurities such a s carbonates, chloride, acetates, water-soluble substances, etc., besides being adulterants may have a n injurious effect upon foliage a n d hence depreciate t h e intrinsic value of t h e material as a spray. Haywood a n d LfcDonnell* have shown t h a t t h e chlorides, sulfates, a n d carbonates of t h e alkali metals render t h e arsenic in certain varieties of commercial lead arsenate more soluble, a n d hence increase t h e liability t o foliage injury. I n order t o make these estimations, new methods were devised a t this Station a n d substituted in some cases where t h e old ones were found t o be inaccurate. Comparisons of t h e methods employed are given in Table I. It can be understood, after a consideration of t h e possibilities for t h e introduction of impurities a n d t h e existence of both arsenic a n d lead in different proportions to form several compounds, t h a t t h e insecticidal values of various commercial arsenates are appreciably different. Recent investigations b y H. F. Wilson,2 Entomologist of this Experiment Station, have shown t h a t t h e arsenates of lead have widely different insecticidal properties. T h e pure lead hydrogen arsenate, specially prepared in this laboratory, was found t o kill more quickly, t o remain in suspension longer a n d t o be more easily applied. From what has been s t a t e d regarding impurities a n d the differences in t h e constitutions of t h e lead arsenates, i t is of paramount importance t o ascertain, a s far as possible, t h e t r u e n a t u r e of t h e commercial arsenates. I n view of t h e possibilities for t h e introduction of impurities a n d adulterations a n d t h e existence of t h e two arsenates in one product, a number of commercial samples were selected a n d a system for their t o t a l analysis devised. T h e following determinations were made: Moisture, t o t a l arsenic oxide, total lead oxide, lead hydrogen arsenate, water-soluble arsenic oxide a n d lead oxide, lead carbonate, water-soluble impurities, chlorides, sulfates, acetates, a n d acid-insoluble impurities. I n order t o make these determinations i t was necessary t o devise several new methods a n d change some of t h e old ones now in use. ANALYTICAL U E T H O D S USED
For t h e determination of 1
moisture, total arsenic
United States Department of Agriculture,
Bureau of Chemistry,
Bull. 131, 46. Proceedings July, 1913. p. 9. 2
of the Entomological
Society of
British
Columbia,
Vol. 7 , No. 6
oxide, a n d t o t a l lead oxide, t h e official method as outlined in Bureau of Chemistry Bull. 107,239, was found satisfactory. Water-soluble arsenic oxide a n d lead oxide were determined by two different methods, one being t h e regular official method as given in Bureau of Chemistry Bull. 107, 2 4 0 , a n d t h e other devised a t this Station which for convenience is designated as t h e “Oregon Station Method.” This method is based upon t h e extreme insolubility of both hydrogen a n d neutral arsenates as shown b y T a r t a r a n d Robinson.‘ It is carried out as follows: A convenient amount, 4 t o 6 grams, of t h e sample is accurately weighed out a n d transferred t o a 590 S. & S. filter paper, first macerating in a mortar with a little water until i t has a consistency t h a t permits pouring onto t h e filter. Distilled water is used t o extract t h e soluble arsenic oxide a n d lead oxide. ( I t is imperative t h a t no carbonic acid nor ammonia be present in t h e water a s they may react with lead arsenate, liberating arsenic in a soluble form.) T h e water-soluble impurities are extracted from t h e sample by washing with hot water until about a liter of filtrate is obtained. It is t h e n cooled, made up t o 1000 cc. a n d a n aliquot t i t r a t e d with s t a n d a r d iodine solution after reduction with potassium iodide according t o modified Gooch and Browning method. Should t h e filtrate come through cloudy i t may be clarified by filtering through a Gooch, t h a t has a thin layer of pure carbon black over t h e asbestos pad. I n t h e estimation of t h e amount of lead hydrogen arsenate in t h e presence of t h e basic salt, i t is first necessary t o remove a n y water-soluble arsenic oxide t h a t may be present. Consequently, t h e residue, obtained b y leaching t h e sample with hot water, in t h e Oregon Station method above, was used. T h e determination was then made b y t h e method devised by T a r t a r and Robinson.’ Water-soluble solids or impurities were also determined b y two different methods. I n one case t h e official method as outlined in Bureau of Chemistry Bull, 107, 2 4 0 , was applied. I n t h e other method employed, zoo cc. of t h e clear filtrate, obtained in t h e Oregon Station method for t h e water-soluble oxide a n d lead oxide as cited above, were evaporated t o dryness in a platinum dish upon a steam b a t h , dried a t 1 1 0 ’ C. a n d weighed. This gave t h e amount of watersoluble solids including foreign impurities a n d t h e soluble arsenic oxide. Lead carbonate was calculated from t h e amount of carbon dioxide found in t h e sample, t h e Bowser method2 being used as a basis for t h e determination of t h e carbon dioxide. T h e procedure, revised a n d made applicable t o lead arsenate, is briefly as follows: An apparatus similar t o t h a t described b y Bowser is used. About I O grams of t h e sample are introduced into a n Erlenmeyer flask of zoo cc. capacity, a n d jo cc. of water added and, after inserting t h e rubber stopper through which a thistle t u b e passes, about 5 cc. of concentrated hydrochloric acid are allowed t o 1 2
Lac. C i l . THISJOURNAL, 4 (1912), 203.
a
June, 191j
T H E J O L 7 R S . l L O F I,VDL-SlRI.4L .I S D E N GI,VE E RI -VG C’H E M I S 7‘R 1-
r u n in. T h e absorbing tower contains j cc. of a j o per cent solution of potassium hydroxide. When all connections are secure a low flame is applied a n d about 2 j cc. distilled over, t i t r a t e d with normal acid t o disappearance of t h e pink color of t h e phenolphthalein indicator, a n d finally with 0 . 1 S acid t o neutrality with methyl orange indicator. E a c h cc. of 0.1 acid used in t h e final titration is equivalent t o o 0 2 6 7 g r a m of lead carbonate,’ P b C 0 3 . T h e acid-insoluble substances were estimated by dissolving I O grams of t h e dry material in warm dilute nitric acid, I O per cent strength. T h e insoluble m a t t e r was collected upon a Gooch, washed free of acidity, dried a t 110’ C. a n d weighed. Chlorides were determined as follows: A convenient a m o u n t of t h e sample, usually 4 grams, was dissolved in warm dilute nitric acid a n d t h e insoluble impurities filtered off. Excess of s t a n d a r d silver nitrate was added t o t h e filtrate a n d titration completed as in t h e T’olhard method for t h e chlorine. -1cetates were tested for qualitatively b y converting t h e m i n t o ethyl acetate a n d observing t h e characteristic odor. This was performed as follo~vs: A convenient a m o u n t of sample was added t o ;t hot solution of j cc. of sulfuric acid a n d j cc. of 9 5 per cent alcohol. This was t h e n brought t o a boil TABLEI-PERCENTAGE Sample No.
Moisture 1. . . . . . . . . . . . . 0.15 2 . . . . . . . . . . . . . 47.08 3 , . . . . . . . . . . . 0.19 4 . . . . . . . . . . . . . 36.69 5 . . . . . . . . . . . . . 53.78 6 . .. . . . . . . . . . 41.35
Total As203
32.53 15.07 31.4i 12.34 12.01 16.19
Total PbO 63.50 34.71 64.02 46.58 30.55 31.64
j01
brands contain small amounts of lead carbonate, free-arsenic oxide, a n d water-soluble impurities. t h e small extent t o which these substances are present are indications of a fair product. Attention is called especially t o Samples 4 a n d 5 which demonstrate t h e value a n d applicability of methods devised a t this Station. Both of these arsenates contain a very high percentage of lead carbonate a n d soluble impurities. Sample 4 contains no lead combined as t h e hydrogen arsenate. Furthermore, since t h e ratio of total arsenic oxide t o total lead oxide in t h e pure basic arsenate is I : 3.19, this sample shows a large excess of lead oxide. This excess could not be accounted for were i t not for t h e detection a n d quantitative estimation of t h e lead carbonzite in t h e sample. T h e absence of water-soluble arsenic oxide should also be noted: obviously this might be expected from a mixture of basic lead arsenate a n d lead carbonate, for t h e presence of lead i n t h e above form would perhaps combine with a n y free arsenic acid, resulting in t h e formation of a n insoluble arsenate. I n fact. t h e absence of watersoluble arsenic oxide in neutral arsenates generally has been demonstrated by analyses of many samples received in this laboratory. Sample 5 , on t h e other hand, is not a lead hydrogen arsenate since t h e ratio of total arsenic oxide t o lead oxide is greater t h a n t h a t in
AKALYSES OF SAMPLES OF COMMERCIAL LEAD ARSEN.4TE
Total PbH.isO4 99.38 30.17 92.01 Trace 18.01 55.97
U’ater soluble AsnOa Oregon Official Station 0.08 0.12 0.08 0.15 Trace Trace Trace Trace 0,ii 1.12 Trace Trace
when. in the presence of a n acetate, t h e characteristic odor of ethyl acetate is obtained. Should there be a n y free acetic acid in t h e sample i t may be leached out with hot water a n d t h e acidity t i t r a t e d against s t a n d a r d sodium hydroxide solution, using phenolphthalein as indicator. The different commercial samples used as exemplary specimens were selected in such a manner t h a t a representative product as manufactured b y various firms was secured. Two of t h e six samples so obtained were t h e d r y powdered t y p e recently placed upon t h e market a n d t h e other four were t h e usual paste arsenates. Z , total analysis of t h e several brands of commercial lead arsenate is given in Table I . A n examination of Table I as a whole shows t h a t t h e commercial arsenates of lead differ t o a considerable extent in their chemical composition. F r o m t h e analysis, Samples I a n d 6 show t h e highest degree of purity, t h e former being almost a pure hydrogen arsenate in t h e powder form, while t h e latter is t h e same kind in t h e paste form. T h e small amounts of impurities present further indicate t h e high grade of both of these products. Samples 2 a n d 3 are mixtures of t h e hydrogen a n d basic salts. t h e hydrogen arsenate predominating in the former sample, a n d t h e basic arsenate in t h e latter. Although both of these 1 The lead may be othernise combined than t h e normal Carbonate b u t since the exact form n a s not ascertained i t is reported as PbCOl
Lead Insoluble carbonate substance Chlorine Sone 0.08 None 0.30 0 04 0.22 0.48 0.13 None 16.5i 0.02 0.06 9.90 0.22 0.10 None 0.04 h-one
Water3oluble impurities Oregon Official station 0.25 0.40 0.35 0.94 0.55 0.71 0.52 0.93 .3.6f, 4.28 0.25 0 55
Watersoluble PbO Xione None h-one Pione h-one ?*Tone
t h e pure salt which is I : 1 . 9 . Analysis shows, furthermore, t h a t this excess of lead oxide is present in t h e form of t h e carbonate. Ynlike Sample .F! i t has a n extraordinary amount of water-soluble arsenic oxide. -It this point, i t might be well t o make a comment upon t h e requirements of t h e Federal Insecticide Law .with reference t o t h e arsenates of lead. I n brief, t h e requirements are: “ I t must not contain: ( I ) more t h a n jo per cent of water; ( 2 ) less t h a n 1 2 . 5 per cent of arsenic oxide, XSZOS;(3) more t h a n 0.75 per cent of water-soluble arsenic oxide, A4s20S.” As stated above, t h e pure hydrogen arsenate as prepared ih t h e laborat o r y , contains 3 2 . 9 8 per cent total arsenid oxide, and in t h e basic or neutral salt there is 2 3 . 4 2 per cent arsenic oxide, these being t h e highest per cents possible in a pure sample. On a jo per cent water basis, therefore, t h e maximum a m o u n t of arsenic oxide possible in a hydrogen arsenate is 16.49 per cent a n d in t h e basic compound 1 1 . 7 1 per cent. Hence, i t is plainly evident t h a t t h e law was made without a sufficient knowledge of t h e exact composition of t h e two types of lead arsenates, for no manufacturer could make a neutral arsenate t h a t contains 1 2 . j per cent total arsenic oxide on a 5 0 per cent water basis when t h e pure product a s prepared in t h e laboratory could contain a t t h e most only 1 1 . 7 1 per cent. I n order t o abide b y t h e law, therefore. i t would be necessary t o reduce t h e moisture
8
502
T H E J O U R N A L O F I N D U S T R I A L A N D ELVGINEERTNG C H E M I S T R Y
or increase t h e arsenic oxide b y some means. T o obviate this difficulty, therefore, a maximum per cent of total arsenic oxide i n hydrogen or acid arsenate should be specified a n d another a m o u n t for t h e neutral or basic arsenate. A comparison of t h e amounts of water-soluble arsenic obtained by each method shows t h a t t h e greater percentage is always found b y t h e Oregon Station method. F r o m these figures i t is obvious t h a t all t h e water-soluble arsenic oxide is not obtained b y t h e official method; nor are t h e results obtained b y t h e Oregon Station method too high, due t o possible hydrolysis or other chemical action upon t h e sample, for in t h e three cases, Samples 3 , 4 a n d 6, where only a trace is reported present b y t h e official method, identical results are obtained b y t h e Oregon Station method. These latter results further substantiate t h e claim made in our previous paper t h a t t h e pure a r senates of lead are extremely insoluble, a n d when there is a n y free-arsenic oxide found i t is due t o t h e arsenic being i n t h e form of a soluble salt a n d not in t h e form of either t h e hydrogen or basic arsenate. It should also be noted t h a t n o soluble lead oxide was found b y either method, which is further proof t h a t t h e water-soluble arsenic oxide was not i n t h e form of a soluble lead salt. As additional proof t h a t all t h e water-soluble arsenic oxide is not obtained b y t h e official method, a glance a t t h e two columns depicting t h e quantity of water-soluble solids or impurities found shows t h a t t h e greater amount is consistently obtained b y t h e Oregon Station method. I t is quite evident from this t h a t all soluble material is not t a k e n out by t h e ordinary official method as outlined in Bureau of Chemistry Bull. 107. I n all cases here cited i t is shown t h a t t h e a m o u n t obtained by t h e Oregon Station method is nearly double t h a t obtained b y t h e official method. It is possible t h a t in t h e official method t h e soluble substances prese n t remained occluded or adsorbed b y t h e arsenate of lead a n d were not removed by water a t room temperat u r e . If, however, successive portions of hot water are used as in t h e Oregon Station method, this difficulty is overcome a n d t h e soluble salts go into solution. I n t h e samples listed in Table I , soluble impurities, in all probability, are composed of chiefly sodium a n d potassium arsenate since qualitative tests show t h e presence of these t w o bases. Other impurities t h a n those found are probably due t o impurities in t h e materials used iri t h e preparation of t h e commercial arsenate. Chlorides were found in three of t h e samples examined. I n two of these cases t h e quantity present was in amounts worthy of note. T h e per cent of acid-insoluble impurities in t h e six samples cited is negligible b u t these impurities should n o t , however, be considered a n unimportant constituent, as other samples received in this laboratory have shown as high as j per cent acid-insoluble material. When present t o t h a t extent i t is a n adulterant of no small consideration. The tests for t h e presence of acetates, a n d sulfates likewise, gave negative results i n these six samples.
Vol. 7 , NO. 6
Other arsenates, analyzed previously in this laboratory, however, have shown t h a t these substances are sometimes present t o a n extent t h a t would depreciate t h e value of t h e arsenate as a n insecticide. T h e detection a n d estimation of these impurities m a y be valuable because their presence with t h e arsenates of lead results in t h e liberation of water-soluble arsenic oxide. SUMMARY
I-The necessity of more complete methods for t h e t r u e valuation of commercial lead arsenates has been pointed o u t . 11-Satisfactory methods have been worked out a n d applied t o commercial samples as follows: I-Estimation of lead hydrogen arsenate i n presence of t h e mixed salts. ’ a-The determination of lead carbonate. 3-New methods for water-soluble arsenic oxide a n d water-soluble impurities. 4-A method for acid-insoluble impurities. 5-The detection of acetates a n d t h e quantitative estimation of chlorides. 111-The application of these methocjs shows a wide variation in t h e composition of t h e commercial arsenates a n d gives a better valuation of t h e m t h a n t h e methods now in use. IV-Comments have been made upon t h e inconsistencies of t h e Federal Insecticide Law. CHEXICAL LABORATORY EXPERIMENT STATION OREGOX AGRICULTURAL CORVALLIS
A STUDY OF VAPORS FROM DRYING PAINT FILMS B y H. H. KING Received April 10, 1915
I n a recent article appearing in THIS JOURNAL,^ N r . C. A. Klein, of hfiddlesex, England, criticized very severely a n article communicated b y M r . H. A . Gardner,* of Washington. M r . Gardner’s communication contained t h e result of a n investigation as t o t h e “ Composition of Paint Vapors.” It cannot be denied t h a t t h e method of procedure in some instances was open t o adverse criticism. Particularly is this t h e case in t h e method employed for determining carbon monoxide. I n Gardner’s method t h e vapors coming from t h e drying oil films were conducted first through fuming sulfuric acid, a n d t h e carbon monoxide t h e n determined b y passing t h e gases through heated iodine pentoxide. I t is a fairly well-established fact t h a t linseed oil films give off formic acid in drying a n d since fuming sulfuric acid decomposes this acid, setting carbon monoxide free, a n y conclusion t h a t t h e monoxide determined h a s come from t h e drying films alone must be lacking in absolute accuracy. T h e point brought o u t b y Klein on this is well taken. T h e present writer has been investigating for eighteen months t h e vapors coming from different drying oils when ground with different kinds of pigments, a n d h a d detected very small quantities of carbon 1
THISJOURNAL, 7 ( 1 9 1 9 , 99.
* Ibid., 6
(1914), 91.
’
