Feb., 1917
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 E NGI iV E E RI N G C H E M I S T R Y
be judged from t h e fact t h a t from jooo kilos of fresh carrots ( 4 7 2 kilos dry) Willstatter a n d Er;cherl obtained only 1 2 5 g. of carotin. This is 2 . : ; parts in IOO,OOO. Chemical tests for colors not infrequently have a delicacy of one part in one billion. T h a t carotin is contained in animal fats a n d oils was abundantly s h m n by t h e work of Palmer and Eckles2 in t h e dairy laborat,ory of t h e University of Missouri, in cooperation with t h e U. S. Department of Agriculture. They showed i t to be contained in butter f a t and t h e body fat obtained from cows, and further t h a t i t was not generated by t h e animal, b u t absorbed from t h e feed, particularly grass. Hence, it is easy t o see why June butter is so highly colored. This work is confirmed b y t h e Department of Internal Revenue3 in t h a t t h e test similar t o t h a t given by palm oil would be given b y a n oleomargarine containing 20 per cent of butter or by oleo oils. This has been further substantiated by t h e work of other chemists. I n view of all these facts i t would seem t o be impossible t o prove t h e presence of palm oil b y this test for e x a m p l e i n alone in a mixture-oleomargarine, which butter (from 5-16 per cent) and oleo oil (45-50 per cent) were present, since all three contain t h e same substance-carotin, t o which t h e characteristic blue color is due. As a result of this work i t would seem t h a t t h e acetic anhydride or acetic acid-sulfuric acid test for palm oil. is n o longer available for use in connection with oleomargarine for t h e following reasons: I-Unreliability of this particular test, no two chemists agreeing upon its interpretation. 11-That t h e test is one for carotin rather t h a n palm oil and may be given by butter, oleo oil or sesame oil-ingredients ordinarily found in oleomargarine. 111-As applied b y t h e Revenue Department, i t is untrustworthy, because interfering oils, as sesame, are not washed out. This communication may be regarded as preliminary, as t h e subject is being further studied. MASSACEIUSETTS INSTITUTE O F TECHNOLOGY, CAMBRIDGE
WET COMBUSTION IN THE NITROSITE COMBUSTION METHOD FOR THE DIRECT DETERMINATION OF RUBBER4 By L. G. WESSON A N D E. S KNORR
I n order t o make more feasible t h e possible use in technical laboratories of t h e nitrosite combustion for t h e direct determination of rubber in rubber goods, we have attempted t h e application of “combustion in t h e wet way” t o this analytical procedure. T h e “nitrosite combustion” method, as described in a previous publication: is based upon t h e formation of t h e “nitrosite” of rubber by t h e action of nitrogen oxide gases upon th.e caoutchouc of t h e sample. This is then separated from other substances (fiilers), a n d Willstiitter and Stoll, “Untersuchungen iiber Chlorophyll,” p. 241. 2 J . B i d Chem.. 17 (1914), 190-249 8 Evidence in court. 1915. 4 This article represents thesis work done b y E. S. Knorr in the course for the degree of Bachelor of Science in Chemistry from the Case School of Applied Science. Read at the 53rd Meeting of the American Chemical Society, New York City, September 25-30, 1916. 6 L. G . Wesson, THISJ O U R N A L , 6 (1914), 459. 1
I39
burned in a specially constructed electrically heated combustion tube. T h e special apparatus and technique required was a decided obstacle t o t h e general use of this method, even should its reliability be demonstrated, and we therefore turned t o “wet combustion” as a n escape from this difficulty. I n t h e course of our experiments, acetone-extracted crude rubber was first used. T h e nitrosite was formed in t h e flask used for t h e combustion, and after t h e complete expulsion of t h e rubber solvent (chloroform), t h e combustion followed in a manner quite similar t o those later described. We obtained as dependable values 96.8, 97.0, 97.6, and 97.1 per cent C10H16, average 97.1 per cent; theoretical, 97.3 per cent C I O H ~ G . I n the regular analytical procedure this simple treatment of t h e nitrosite is not possible since t h e latter must be separated from t h e mineral matter and other impurities b y t h e use of some solvent after filtration from t h e chloroform. We first used a solvent acetone, which was added t o t h e dry nitrosite in t h e combustion flask. The acetone was first evaporated off, then t h e flask was heated I ~ / Z hrs. b y a boiling water b a t h while a current of dry air passed slowly through t h e flask. The value now obtained (100.7 per cent) upon combustion, indicated a retention of acetone. A repetition of this experiment with t h e use of only ethyl acetate as solvent gave 96.4, 97.1, a n d 97.0 per cent CloHiG. These figures were more promising. Moreover, t h e ethyl acetate on evaporation left t h e residual nitrosite in a more porous, and thus more favorable, condition for rapid expulsion of t h e organic solvent t h a n did t h e acetone. Ethyl acetate was therefore adopted as t h e solvent in all of t h e analyses of vulcanized rubber. T h e use of acetic ester did not, however, eliminate our troubles with retained solvent, as we found when we next turned t o t h e analysis of compounded rubber samples, instead of t h e raw gum. We believe t h a t this difficulty explains most of t h e erratic results we had t o t h e end of our work. We believe t h a t we have now found t h e remedy for this retention of solvent in t h e addition of water, containing a drop of hydrochloric acid, t o t h e nitrosite, and subsequent evaporation of this t o dryness, after all solvent has been removed in t h e ordinary way. I n a sample’ compounded with 35.0 per cent Fine Para, using the method described, we found 34.7, 34.9, 34.8, a n d 34.2 per cent C10H16, average 34.7 per cent; theoretical, 34.4 per cent C ~ O H ~ G . I n a sample’ compounded with 40.0 per cent plantation rubber, we found 38.9, 39.8, 37.9, 38.1, a n d 37.7 per cent C10HI6, average 38. j per cent; theoretical value, 38.3 per cent CioHi~. PROCEDURE PREPARATION
OF
THE
NITROSITE
FOR
THE
COY-
BusTIoN-After the rubber sample has been ground g. in a meat chopper t o pass a 2 0 mesh sieve, and of i t extracted 3 hrs. with acetone and ‘ / 2 hr. or longer with chloroform, t h e extracted sample is allowed 1
Theee samples were kindly sent us b y the Bureau of Standards
140
T H E J 0 U R A V . I L O F I l 1 7 D I ; S T R I A L A,VD E~VGINEERI~\TGC H E M I S T R Y
t o dissolve in. or thoroughly absorb, chloroform. A small Florence flask ( 7 5 cc.) is used, which may be about one-half full of t h e solvent. Nitrous oxide vapors, evolved from dilute nitric acid (sp. gr. 1.3) and arsenic trioxide: are then passed through t h e cooled chloroform until t h e deep green color becomes permanent for about I j min., and t h e whole allowed t o stand over night for completion of t h e action. The chloroform i.5 then decanted through a dry Gooch crucible and asbestos matte (the former rests in a n ordinary 60' filter funnel) into t h e combustion flask, from which t h e chloroform is then evaporated by means of a boiling water b a t h and a dry air current.' hIeanwhile t h e residue in t h e Florence flask has been similarly dried. The separation of fillers and nitrosite is now brought ahout in t h e following way: Small portions ( j cc.) of calcium chloride-dried ethyl acetate are added t o t h e residue in t h e Florence flask, t h e latter warmed, and t h e liquid decanted through t h e Gooch crucible into t h e combustion flask! repeatedly. until t h e filtrate runs through entirely colorless. ,%fter evaporation of t h e acetate (recovery of t h e solvent as well), t h e residue is carefully freed from solvent by warming t h e containing flask in a boiling water b a t h for 'about I j min., after which I j cc. of water, containing I drop conc. HC1, is added, and quickly evaporated by t h e use of a boiling calcium chloride b a t h and brisk current of dry air. The heating is continued a t least ' / ? hr. after t h e residue is again apparently dry. T H E c o m r s T I o x A P P A R A T U S consists of a 2 0 0 cc. round-bottom distilling flask, which is provided with a dropping funnel (100 cc.) through a one-hole rubber stopper, and a series of U-tubes containing in order, ( I ) conc. H2SO4-K2Cr207, renewed every I or 2 combustions, ( 2 ) water containing a drop of t h e preceding, (3) granular zinc, (4) calcium chloride, (j) soda-lime (weighed)! (6) soda-lime and calcium chloride (weighed). T H E conmusTIoP-The weighed soda-lime tubes in position, a n d t h e combustion flask cooled by water, a Volume ( 2 0 cc.) of cooled concentrated sulfuric acid is run rapidly into t h e flask onto t h e nitrosite; then t h e cooled oxidizing solution of I O g. pulverized K2Cr207in 7 j cc. conc. HzS04, in a very slow stream. The flask may now be gently warmed by a sand b a t h t o obtain a moderately rapid evolution of gas.? This is done as long as gas continues t o be evolved (about a n hour), when a carbon dioxide-free current of air, t h e heating being maintained, is passed via t h e dropping funnel through t h e apparatus for at least '/* hr. t o sweep all carbon dioxide into t h e soda-lime tubes.
W t . COS X
136 440
X
zoo
gives percentage
C10H16in t h e sample. We hope? in conclusion, t h a t further study and im1 Mr. J. H . Tuttle of the Bureau of Standards has found that the chloroform-soluble residue thus recovered may be very appreciable, and i t is to his suggestion t h a t this modification is dlie. ' T h a t carbon monoxide is formed during the combustion can be shown by allowing the gases which have passed the absorption train to come in contact with heated copper oxide a n a then barium hydroxide solution. A precipitate ensues, but the amount is not appreciable for the results of the analysis.
5'01. 9 , N O . 2
provements of this method will eventually give a reliable and not too difficult procedure for the direct determination of rubber, not only in good quality compounds but also in factis and other inferior substitute-containing rubbers. CASE: S C H O O L OF APPLIED S C I E S C B CLEVELAND, OIIIO
DETERMINATION OF MINERAL FILLERS IN RUBBER ANILINE METHOD By OTTO H. KLBIN, J
O H ~ H.
LINK AND FRANKGOTTSCH
Received October 23, 1916
Although the use of aniline as a solvent for vulcanized rubber is not new, there is very little information t o be found concerning such use in t h e literature. We have. therefore, thought t h a t a n account of t h e method as far as i t has been worked out. together with some analyses of samples of known composition, mould be of interest. This report should be considered as a preliminary one, as t h e supply of rubber mixings a t hand for our experiments was limited and other rubber fillers t h a n those used are yet t o be experimented with. I n making t h e determination it is essential t h a t t h e sample be finely powdered ( 2 0 mesh). A I-gram sample is extracted with acetone for 4 hours, dried a t a low temperature, a n d then transferred to a weighecl I O O cc. centrifuge tube. The residue is covered with jO cc. of pure aniline, j cc. of nitrobenzene added, the mixture stirred, covered, and heated a t 160' C. with occasional stirring until solution is complete. I t is our practice t o heat t h e samples over night in a Freas oven. I n most cases solution is complete by t h e next day. Sometimes the sample dissolves in 3 t o 4 hours. If t h e rubber is not yet in solution, this can be seen by stirring with a glass rod. When solution is complete, there is nothing t o be seen b u t fine pigment, free from rubbery appearance.' T h e tube is allowed t o cool sufficiently, filled up with ether a n d well stirred. I t is then centrifuged for I j minutes a t Ijoo r. p. m. The supernatant liquid is decanted, about 2 5 cc. of ether added and t h e pigment stirred up completely. It is centrifuged again a n d t h e decantate added t o t h e first. Four such washings with ether are necessary. The tube is dried a t 100' C., cooled and weighed. The united decantates are evaporated a n d then ignited in a weighed porcelain or silica dish; t h e weight of fillers found is added t o t h a t in t h e tube. The percentage of fillers plus t h a t of total acetone extract is subtracted from I O O per cent, and t h e difference recorded as rubber gum. Aniline differs from other solvents in t h a t rubber dissolved in i t forms a thin solution which permits t h e mineral fillers t o separate readily. The small amount of nitrobenzene used, causes a more rapid solution. I t was found t h a t semicured compounds dissolve more slowly t h a n thoroughly cured soft stocks or very hard ones. With undercured compounds a soft pasty mass is formed, which 1 The chemist who makes the analysis for the first time may be uncertain of himself a t this point, but after one or two determinations have been made he will a t once recognize any undissolved rubber.
