3 26
T H E J O C ' R Y A L O F I . V D C S T R I A L AAVD E L T G I S E E R I X C C I i B - U I S T R Y
obtained on Sample I , t h e y are sufficiently accurate f o r all practical purposes. t h e maximum error o n sulfur being only 0.11 per cent. Results slightly higher t h a n those calculated m u s t be expected, since SampIes 1 3 a n d 16.which contain b a r i u m sulfate a n d n o b a r i u m carbonate, yield small a m o u n t s of precipitate b y this m e t h o d , p a r t l y i n consequence of slight reduction of b a r i u m sulfate t o sulfide during t h e ignition of t h e r u b b e r . a n d p a r t l y on account of t h e slight action of a m m o n i u m carbonate on b a r i u m sulfate. These amounts! in themselves. ? r e negligible. It is a p p a r e n t , therefore, t h a t neither lead sulfate nor b a r i u m sulfate interfere appreciably with t h e determination of b a r i u m carbonate b y this procedure. X E T H O D F I X A L L Y ADOPTED--The total barium in t h e rubber compound is determined as b a r i u m sulfate b y t h e method for the determination of barytes i n usc a t this Bureau.' T h i s m e t h o d was first suggested b y C. E . Waters, a n d afterwards modified b y R.H . S m i t h a n d t h e a u t h o r . B a r i u m carbonate is determined i n a separate sample b y t h e m e t h o d just described, a n d a n equivalent a m o u n t of b a r i u m sulfate is deducted f r o m t h e t o t a l b a r i u m sulfate. T h e sulfur in t h e remaining, portion of b a r i u m sulfate is calculated, a n d t h e t o t a l sulfur determination is corrected b y this amount,
s r3131.4 K Y
-1nen- method is given for t h e determination of b a r i u m carbonate in vulcanized rubber goods. I t is shown t h a t this method is sufficiently accurate in t h e presence of lead a n d b a r i u m sulfates. 'The a u t h o r wishes t o acknocvledge t h e assistance of l l r . H . -1.E h r m a n of this Bureau. who T-ery kindly compounded a n d vulcanized t h e samples used in this investigation. I ~ u R I ~ A OF' U S T A S D A K U C - , \TASE!I>TGTON
A METHOD FOR THE DIRECT DETERMINATION OF THE RUBBER IN A COMPOUND B y ROBERTIT. BELFIT
Received December I , 1915
A t present all published methods (with t h e exception of TT'esson's "combustion method")' for determining t h e percentage of t h e rubber in a compound) are ina d e q u a t e . 'The most used m e t h o d is t h e indirect one in which t h e sample is analyzed for fillers. t o t a l sulfur, a n d waxy hydrocarbons, a n d t h e "rubber" is considered as t h e difference between IOO a n d t h e s u m of t h e three corrected percentages. As this m e t h o d depends upon t h e accurate determinations of t h e fillers, total sulfur, a n d waxy hydrocarbons, i t is unsatisfactory. for it is doubtful if exact methods exist for t h e determinations of t h e fillers a n d maxy h y d r o c ar b o n s . -1n u m b e r of direct methods have been proposed which depend -upon t h e formation of known compounds, such as nitrosates, nitrosires, or bromides; b u t t h e exact formulas of these compounds are not constant or controllable. Therefore, these methods ; I3ur of Standards. Civc. 38 (1915), 68, 3rd Ii.orld, 51 (1914). 128.' THIS J O C R N A L , 6 (1914), 459.
Ed.;
I n d i a Rubber
IT0l. 8.
NO.4
are at present valueless for t h e estimation or' the rubber in vulcanized goods. bIr. L. G. Tl'esson in his method forms a nitrosite of t h e rubber, but only in order t b obtain a product soluble in acetone. He t h e n separates t h e fillers, takes a n aliquot portion of t h e solution, evaporates off t h e solvent, and finally b u r n s t h e nitrosite in ;L current of oxygen. F r o m t h e carbon dioxide formed, h e calculates t h e percentage of t h e rubber according t o t h e equation CIoH16 --+ I o C O ~ . This method appears t o give good results. b u t it is rather long a n d intricate. due t o t h e necessity of forming a nitrosite a n d of handling t h e viscous riihber solutions. T h e method presented in this paper is of t h e combustion t y p e a n d is considered simple, quick. and accurate for high-grade compounds. I n brief, :I charge of t h e finely ground rubber is extracted w i t h acetone, dried, t r e a t e d with hydrochloric acir! t o decompose all carbonates, again dried, after which a portion is burned t o carbon dioxide, from which t h e percentage of rubber is calculated. PROCEDURE
T h e sample is ground so t h a t it all passes through a 2 0 mesh sieve while b u t 2 0 per cent passes through a 40 mesh sieve. Then! 2 g. are extractctl for j hrs. with acetone in a n a p p a r a t u s in n-hich t h e solvent is continually a t t h e boiling point. T h e residue is now placed i n a weighed t u b e if not a l r r a d y in one. This t u b e containing t h e residue is inscrtctl in a n oven, kept a t 100' C . . a n d a current of dry carbon dioxide is passed through t h e t u b e in order t o aid rapid drying a n d prevent oxidation. 'The dried sample is weighed, and t h e percentage loss in weight calculated. About one-half of this extracted sample is weighed o u t into a 2 5 0 cc. Erlenmeyer flask. where it is cautiously boiled for 3 0 min. with r j o e?. of HCI ( I : j by v o l . ) . I n this process all carbonates a r e driven off. S o w , t h e liquid is decanted through a n a l u n d u m crucible on a suction: and t h e residue is washed three times b y decantation with mater a t a b o u t 6 0 " C. T h e rubber substance is t h e n transferred t o t h e crucible a n d washed t e n more times with m-aim water, T h e residue is now placed in a t u b e l a n d dried in a s t r e a m of d r y carbon dioxide a t 100' C . for two t o four hours, T h e t u b e is t h e n remol-ed and allowed t o cool in a desiccator. T h e resulting residue is now transferred t o a v-eighing t u b e , from n-hick 0.3-g. samples are 1%-eighed f o r t h e final process, t h a t of combustion. T h e combustion is carried out in approximately t h e same manner as for a n y organic compound, except t h a t no reduced copper spiral is used, as t h e water a n d nitrogen oxides are absorbed in a concentrated solution of pot dichromate in sulfuric acid. \-esse1 of small volume is necessary for this solution, or otherwise it is almost impossible t o displace all of the carbon dioxide niter < in inside diameter 1 T h e author uses a tube about 2 in. long a n d with t h e lower third constricted to I in. inside diameter.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Apr., 1916
t h e sample has been completely burned. Beyond this t u b e is placed a U t u b e containing zinc d u s t t o absorb all possible acid gases other t h a n carbon dioxide. T h e potassium hydroxide absorption bulb is next and last in t h e train. T h e rubber substance is burned in a s t r e a m of oxygen, a n d t h e potash bulb is always weighed when full of oxygen. CIDHItj + IOCOZ This method on pure, fine p a r a g u m gave 96.19 a n d 96. j 7 per cent (av. 96.38). T h e value of 0.96 was t h e n used as t h e figure b y which t h e weight of ClaH16 should be divided in order t o obtain t h e weight of t h e rubber from which it came. This factor was used o n t h e compounds m a d e with other varieties of gums without determinations o n those gums, as t h e factor would be valueless unless it applied t o all high-grade rubber gums. SAMPLE CALCELATION Loss due t o acetone extraction - 5.45 per cent Weight extracted with HC1 - 0.9850 g. Weight after HCI extraction - 0.6483 g . Weight burned - 0.2824 g. Weight of COS absorbed - 0.4232 g.
136x0 4232 = W t 440
of CioHin burned
-__ l : ~ O x x = OW ~ t .~of~rubber burned 136 0'4232 0'6483 = R = W t . of rubber t h a t would have been 440 X 0.96 X 0.2824 burned if all t h a t extracted with HC1 was burned
&'ow
-_ l,oOOo0.985OP - 0,0545 = W t . of unextracted sample which contained R
grams
of rubber 136 X 0.4232 X 0.6483 X 0.9455 .. . ___ 440 X 0.96 X 0.2824 X 0.9850
= 30,01 per cent
ANBLYTICAL RESGLTS
30 Per cent Fine Para Stock 30.31 30.12
....
--
Av.. 30.22
30 Per cent Cameta Stock 30.01 30.38 29,60
31 Per cent Ceylon Stock (Red Oxide) 30.50 30.87 ..., --
_-
30 00
30.69
30 49
__
31 Per cent Ceylon Stock (Black) ~, 30.18 30.80
....
COIiCLUSIOh-S
This method is found applicable t o high-grade compounds which do n o t contain lampblack, shoddy, or rubber substitutes. If t h e compound should cont a i n lampblack, it is shown by t h e dark color of t h e g u m when t r e a t e d with dilute hydrochloric acid. Otherwise, t h e g u m is grayish white. T h e presence of shoddies a n d rubber substitutes m a y be detected, respectively, b y t h e d a r k color of t h e acetone extract or a high alcoholic potassium hydroxide ( K O H ) extract. Should t h e described method be used alone for specification work, t h e percentage of rubber could be made t o appear falsely high b y adding ground leather, starch, egg albumen, or some other organic compounds which are insoluble in acetone, water, a n d dilute hydrochloric acid. But t h e addition of such substances would decrease t h e quality of t h e comp o u n d a n d probably their presence could be detected b y qualitative chemical means or physical testing. Therefore, even though this method is at present restricted t o positively high-grade stocks, it is felt t h a t its use m a y be made more general after further experimentation. RHODEISLAND STATECOLLEGE
KINGSTON
327
THE REDUCTION OF AsV TO Asiii BY CUPROUS CHLORIDE AND THE DETERMlNATION OF ARSENIC BY DISTILLATION AS ARSENIC TRICHLORIDE By R . C. ROARK AND C. C. MCDONNELL Received October 15, 1915
For t h e determination of arsenic in arsenical insecticides, t h e Association of Official Agricultural Chemists has adopted methods for Paris green, London purple, and lead arsenate on1y.l I n recent years there have been placed on t h e market other arsenical insecticides, such as t h e arsenates a n d arsenites of calcium a n d zinc, a n d combinations of fungicides a n d insecticides which contain arsenic, such as Bordeauxlead arqenate, Bordeaux-Paris green, Bordeaux-zinc arsenite, etc. I n attem,pting t o find a m e t h o d for t h e quick a n d accurate determination of arsenic in these products, recourse was h a d t o t h e well-known distillation m e t h o d , * using ferrous sulfate as a reducing agent. This m e t h o d was carried o u t as fo!lows: An a m o u n t of t h e sample containing n o t over 0.j g. arsenic calculated as AslOe a n d I O g. of ferrous sulfate was transferred t o a 500, cc. distilling flask, I O O cc. concentrated hydrochloric acid (sp. gr. 1.19) added, t h e solution heated t o boiling a n d t h e vapors distilled through a wellcooled condenser into t h e arrangement of flasks shown in Fig. I. When t h e volume in t h e distilling flask was reduced t o about 4 0 cc., a n additional jo cc. of concentrated hydrochloric acid was added b y means of a dropping funnel. This process was continued until 2 0 0 cc. of acid had distilled over. T h e distillate was t h e n m a d e u p t o I liter in a graduated flask, a n aliquot of zoo cc. taken, nearly neutralized with a concentrated solution of sodium hydroxide, sodium bicarbonate added in excess, a n d t h e arsenic trioxide t i t r a t e d with a n approximately N ; 2 0 iodine solution, using starch paste as a n indicator. On analyzing a commercial d r y lead arsenate in this way, only 26.3 per cent AszO:, was found) whereas by t h e Official method2 31.9 per cent was obtained. This low result was somewhat surprising in view of t h e fact t h a t distillation of samples of Bordeaux-lead arsenate with ferrous sulfate a n d hydrochloric acid had yielded t h e s a m e a m o u n t of arsenic as other methods. I n order t o see if t h e copper salts present in t h e samples containing Bordeaux had a n y effect on t h e results, another distillation of this lead arsenate was made, with t h e addition of j g. crystallized copper sulfate t o t h e I O g. ferrous sulfate. Distilling as before, 31.8 per cent A s 2 0 j was found. Cuprous chloride, as suggested b y Olsen,3 was t h e n tried as t h e reducing agent, when, using t h e same procedure as before, 32.0 per cent A s 2 0 5was obtained. I n order t o test this method further, a s a m p l e ' o f pure lead hydrogen arsenate4 (PbHAsOd) was analyzed Bur. of Chem., Bull. 107, Rev. (19081, 25-6. 28-9, 239; Bull. 132 (1910), 43-4; Jouv. A . 0. A . C., 1 (1915), 444-6. Bur. of Chem., Bull. 107, Rev. (1908), 239. 3 "Quantitative Chemical Analysis," 1910, p. 139. Prepared b y McDonnell and Smith, for use in another investigation, by precipitating potassium dihydrogen arsenate, KHnAsOa, with lead nitrate and recrystallizing from nitric acid.
