3 24
T H E J O U R M A L O F I N D C ' S T R I A L ALVD E N G I N E E R I N G C H E N I S T R Y
second fusion of such oxides gave no further carbon dioxide t o a freshly filled a n d clear barium hydroxide tube. Great care was taken a t all stages of t h e work t o eliminate extraneous carbon dioxide or other substances t h a t would cause a blank, so t h a t , as already stated, t h e blank was always negligible. The frequent blanks which were made during this work myere carried out ( I ) without a n y steel in t h e furnace; ( 2 ) when burning B. of S. Standard Steel No. 2 3 , which, as shown in t h e table of results in this paper, gives identical values when burned in the ordinary way a n d b y our modified method. The fused oxides were readily remo1Ted from the boats, in preparation for t h e next combustion, b y digesting in strong hydrochloric acid for a few hours. The results in t h e table show t h a t some steels give higher results b y the new method t h a n are shown on t h e certificates, others yield only slightly higher figures a n d still others give the same results b y both methods. We find it impossible to relate these three classes with t h e size of drillings used, with t h e carbon content of t h e sample, or especially, with t h e presence or absence of t h e usual alloying elements. In only t w o cases were t h e results by the modified method as much as 0 . 0 2 per cent higher t h a n the certificate value; with most of t h e other samples t h e difference was of t h e order of 0.01per cent. Our work does n o t cover the Bureau's complete series of standard analyzed steels and irons, b u t t h e results are deemed quite representative, a n d we believe t h e y are complete enough t o justify us in t h e conclusion t h a t t h e certificate values for these steels cannot be affected with a n error greater t h a n 0.01j per cent (probably minus), a n d in most cases t h e error is much less. I t is believed t h a t such errors are negligible, considering t h e uses to which these standards are a t present being put. T h e experimental difficulties a n d t h e inconvenience of this method of determining carbon place it beyond t h e reach of most industrial and works laboratories, a n d we do not, therefore, recommend its use t o such, except in t h e case of products for which it may be found better adapted t h a n other methods. BCREAUOF STANDARDS, WASHINGTON
AN ACCURATE END-POINT IN THE VOLUMETRIC DETERMINATION OF SULFUR IN STEEL By HERBERTZSCHIEGNER Received November 26, 1915
The following method was devised with the object of eliminating the inaccuracies due t o t h e varying shades of t h e blue color of t h e starch iodide formed in t h e titration of hydrogen sulfide with iodine. While it depends primarily on t h e production of starch iodide, as does t h e former method, the actual blue color is disregarded. In t h e experimental evolution of this end-point a standard solution of potassium iodide and iodate was used, together with a n ammoniacal solution of cadmium chloride as a n absorption medium and a solution of wheat starch as indicator. The iodine or iodate solution is made slightly stronger t h a n usual a n d is standardized against a steel of known sulfur content.
Vol. 8,
Xo.4
This deviation from the usual method is in use in our laboratory and yields very good results. The starch solution found to give t h e best results is made b y rubbing t o a paste with water, 1 2 g. of wheat starch and pouring the mixture into z liters of boiling water in which is dissolved 3 g. of potassium or sodium hydroxide. Two cc. of this solution are measured from a pipette or burette for each titration. Starch solution thus prepared will keep indefinitely and is not subject t o t h e salting out of t h e colloidal starch which is t h e case when zinc chloride is added as a preservatire. T o obtain uniform results a standard m o d u s o p e r a n d i must be adhered t o . The volume of the HC1 used t o decompose the CdsS, t h e volume of t h e indicator, and t h e volume of the final solution must equal t h e volumes of t h e solutions used in standardizing t h e iodine or iodate solution. A special titrating vessel is required, consisting of a white porcelain beaker, about 7 cm. in diameter and 16 cm. in depth. On the bottom of this beaker (inside) is cemented a thin, black disc of hard rubber or celluloid about 2 cm. in diameter. ( A substitute for this vessel may be made b y painting t h e black spot on the outside of a glass beaker, then covering the whole outside of the beaker with white enamel; t h e black spot should t h e n appear sharply defined against the white of t h e beaker.) The determination is carried out as usual until t h e titration is commenced, t h e n t h e black spot is carefully observed, and as the solution darkens t h e iodine is added carefully with agitation. Finally a point will be reached when one drop of iodine will render t h e 'spot invisible on allowing t h e solution t o come to rest. This is t h e end-point and t h e burette reading may now be taken. Owing to the milkiness of t h e solution when high sulfur iron or steel is being analyzed the black spot may not a t first be apparent b u t will become plainly visible when t h e titration is about four-fifths completed a n d will remain so until t h e last drop of iodine renders it invisible. T h e end-point is sharp and the results in terms of per cent do not vary more t h a n 0,001. An incandescent lamp may be placed a t such a distance from t h e titrating vessel t h a t t h e same results will be obtained with artificial light as with daylight. The light should not be situated directly over t h e beaker b u t t o one side of it. AMERICANLOCOWOTWE COMPANY SCRBNECTADY,N. Y.
THE DETERMINATION' OF BARIUM CARBONATE AND BARIUM SULFATE IN VULCANIZED RUBBER GOODS' By JOHN B. TUTTLE Received November 17, 1915
With t h e advent of buying rubber goods on specifications i t became necessary t o develop methods which would accurately determine the various constituents. One of the most important determinations is t h a t of total sulfur. I n a recent publication of this Bureau,2 the sulfur-bearing constituents of vulcanized rubber 1 2
Published by permission of the Director of the Bureau of Standards. Bureau of Standards, Technologic Paper, 46; THIS J O U R N A L , 7
(1915). 6 5 8 .
Apr., 1916
T H E JOCRAV.4L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
goods were mentioned, a n d a method was given for a quantitative determination of t h e sulfur which t h e y contain. I n this article, it was stated t h a t sulfur may occur in variobs forms, including metallic sulfates, usually lead a n d barium. M a n y specifications now permit t h e use of barium sulfate (barytes) without having t h e sulfur which i t contains count as part of t h e specified total sulfur. It is therefore necessary t o be able t o determine t h e percentage oE this mineral. This was not at all difficult as long as t h e rubber compounds contained barium only in t h e form of t h e sulfate. When, however, manufacturers began using t h e carbonate as well as t h e sulfate, t h e problem became much more complex, since i t became necessary t o determine both salts of barium in t h e presence of each other, as well as in t h e presence of other sulfurbearing minerals. It is with this phase of t h e problem t h a t the present article deals. T h e separation of barium carbonate from barium sulfate in the absence of other minerals is readily accomplished by solution of t h e carbonate in acids such as hydrochloric, acetic, etc. I n rubber compounds, however, this method is not applicable, since lead sulfate may be present, in which case part of t h e lead sulfate will also be dissolved; t h e reaction between t h e lead sulfate in solution a n d t h e barium will cause t h e precipitation of barium sulfate, so t h a t t h e results.obtained will b e low. Lead sulfate may be dissolved in ammonium acetate, a n d i t was thought t h a t this disturbing constituent could be eliminated b y this procedure, which, however, was found t o be too slow a n d unreliable t o be a n acceptable method. However, still another procedure is available, v i z . , transforming t h e lead sulfate t o t h e carbonate b y boiling with alkaline carbonates, a n d filtering off t h e soluble sulfates. Sodium carbonate readily converts lead sulfate a n d barium sulfate' into their carbonates; ammonium carbonate reacts with lead snlfate, b u t tests made here show t h a t i t has only a slight effect on barium sulfate. By t r e a t m e n t with ammonium carbonate, we can therefore change t h e lead sulfate into t h e carbonate, a n d t h e n filter t h e soluble sulfates from t h e lead carbonate, barium carbonate a n d barium sulfate. Calcium a n d zinc carbonates, which may be present, do not interfere with t h e desired separation. SAMPLEs-The four samples used in this investigation were of known composition (Table I ) , having been compounded a n d vulcanized a t this Bureau. The barium carbonate used in Nos. I a n d 1 7 was TABLE I-COMPOSITION OF SAMPLES COMPOUND No. 1 h'o. 13 No. 16 Fine Para Rubber . . . . . 39.6 30.0 20.0 Plantation Rubber. . . . . . . ... ... 2.5 3.0 2.0 Sulfur. . . . . . . . . . . . . . . . 8.6 7.0 8.0 Litharge., . . . . . . . . . . . Zinc Oxide. . . . . . . . . . . 8.7 20.0 20.0 ... ... Sublimed White Lead.. 30.6 Barium Carbonate.. . . . 10.0 ... ... 20.0 30.0 Barium Sulfate.. . . . . . . . . . Whiting. . . . . . . . . . . . . . . . . 20.0 20.0 Vaseline.. . . . . . . . . . . . . . . . ... ... Total Per cent.. . . . .
No 17
...
40.0 4.0 8.0 15.0 .
.
I
10.0 20.0
...
3.0
_ _ _ _ _ _ _ _ 100.0
100.0
100.0
100.0
Merck's best quality, a n d was finely ground before compounding. T h e barium sulfate was tested a n d found t o contain practically n o soluble barium salts. 1 Noyes and Bray, J . A m . Chem. Soc., 29 (1907), 151. state that 80 per cent of barium sulfate is converted into barium carbonate when boiled with an excess of sodium carbonate.
325
It will be noted t h a t No. I contained both barium carbonate a n d lead sulfate, No. 1 7 barium carbonate a n d barium sulfate, while Nos. 13 a n d 16 contained barium sulfate only. M E T H O D EMPLOYED-Schaeffer' has shown t h a t t h e organic matter in rubber can be removed b y ignition in a n atmosphere of carbon dioxide without change of sulfur t o sulfide, or of either t o sulfate. Slight reduction of barium sulfate to 'sulfide may occur during ignition of t h e rubber, b u t experience shows t h a t t h e a m o u n t of sulfide formed is practically negligible. T h e apparatus used for t h e decomposition of t h e rubber was practically t h e same as t h a t used b y Schaeffer, the only change being that t h e sample was placed in a porcelain boat so as t o facilitate t h e removal of t h e residue from t h e glass tube. One gram of t h e rubber was taken for each determination. After ignition a n d cooling in carbon dioxide, t h e boat was removed, t h e residue finely ground in a n agate mortar, transferred t o a 2 5 0 cc. beaker, a n d treated with 5 t o I O g. ammonium carbonate, 15 t o 2 0 cc. of strong ammonia water a n d about 50 cc. of distilled water. TABLE11-RESULTS OF BARIUMCARBONATE DETERMINATION (All results are expressed in percentages of the original sample.) Sample CONSTITUENTS PRESEXT -FOUND9.98 10.02 9.72 9.67 1 Barium Carbonate 10.0 1.62 1.63 1.58 1.57 Sulfur equivalent t o BaCOa 1.63 10.28 9.76 10.73 10.71 17 Barium Carbonate 10.0 1.74 1.74 Sulfur equivalent t o BaCO a 1.63 1.67 1.59 n 17 0.25 13 Barium Carbonate .......... 0 . 0 0.17 0.08 0.03 Sulfur equivalent t o BaCOa 0 . 0 0.03 0.01 0.03 0.09 0.0 0.29 0.19 0.31 16 Barium Carbonate 0.02 0.05 0 . 0 3 0.05 Sulfur equivalent t o BaCOs 0 . 0
.......... ..........
-. ..
..........
T h e mixture was boiled for 1 5 t o 30 min., filtered, a n d t h e precipitate thoroughly washed t o remove all soluble sulfates. T h e residue on t h e filter paper was washed back into the original beaker with distilled water; about I O cc. of glacial acetic acid a n d sufficient water t o make t h e total volume of t h e solution about IOO cc. were added. This was heated to boiling a n d t h e n filtered through t h e same filter paper as before. By this procedure, lead, barium, calcium a n d zinc carbonates pass into solution while barium sulfate a n d lead sulfide are not attacked. Hydrogen sulfide was passed into t h e filtrate, t h e lead sulfide filtered off, t h e filtrate heated on the steam bath, a n d I O cc. of I O per cent sulfuric acid added. The solution was allowed t o s t a n d over night on t h e s t e a m b a t h ; the next d a y t h e precipitate was filtered off, ignited in a porcelain crucible, cooled a n d weighed. DISCUSSION O F R E S U L T S
T h e barium sulfate (Table. 11) was calculated t o barium carbonate, using t h e factor 0.845. T h e sulfur in t h e barium sulfate was also calculated, since i t is desirable t o know just what error will be introduced if t h e barium present in t h e form of t h e carbonate should be considered as being present as t h e sulfate. T h e results on Sample I show t h a t in t h e presence of lead sulfate (in t h e sublimed white lead), barium carbonate can be determined with accuracy, t h e results, expressed in terms of sulfur, being within 0.06 per cent of t h e calculated amount. I n Sample 1 7 , we have present both t h e sulfate a n d carbonate of barium, a n d while t h e results are not as good as those 1
THISJOURNAL, 4 (1912). 837.
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 for all practical purposes. t h e maximum error on sulfur being only 0.11 per cent. Results slightly higher t h a n those calculated must be expected, since SampIes 1 3 a n d 16.which contain barium sulfate and no barium carbonate, yield small amounts of precipitate b y this method, partly i n consequence of slight reduction of barium sulfate t o sulfide during the ignition of t h e rubber. and partly on account of t h e slight action of ammonium carbonate on barium sulfate. These amounts! in themselves. ? r e negligible. It is apparent, therefore, t h a t neither lead sulfate nor barium sulfate interfere appreciably with t h e determination of barium carbonate b y this procedure. XETHOD FIXALLY ADOPTED--The total barium i n t h e rubber compound is determined as barium sulfate b y t h e method for the determination of barytes i n usc a t this Bureau.' This method was first suggested b y C. E . Waters, and afterwards modified b y R.H . Smith and t h e author. Barium carbonate is determined i n a separate sample b y t h e method just described, a n d a n equivalent amount of barium sulfate is deducted from t h e total barium sulfate. T h e sulfur in t h e remaining, portion of barium sulfate is calculated, and t h e total sulfur determination is corrected b y this amount, s r3131.4 K Y -1nen- method is given for the determination of barium 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 and barium sulfates. 'The author 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 and 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 in-
adequate. 'The most used method is t h e indirect one in which t h e sample is analyzed for fillers. t o t a l sulfur, and waxy hydrocarbons, and 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 method depends upon t h e accurate determinations of t h e fillers, total sulfur, and waxy hydrocarbons, it is unsatisfactory. for it is doubtful if exact methods exist for t h e determinations of t h e fillers and maxy hydro c ar b o n s . -1number 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 then separates t h e fillers, takes a n aliquot portion of t h e solution, evaporates off t h e solvent, and finally burns t h e nitrosite in ;L current of oxygen. From t h e carbon dioxide formed, he 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. but it is rather long and intricate. due t o t h e necessity of forming a nitrosite and of handling t h e viscous riihber solutions. The method presented in this paper is of t h e combustion t y p e and 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, treated 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 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 apparatus in n-hich the solvent is continually a t t h e boiling point. The residue is now placed i n a weighed t u b e if not alrrady in one. This t u b e containing t h e residue is inscrtctl in a n oven, kept a t 100' C . . and a current of dry carbon dioxide is passed through t h e tube in order t o aid rapid drying and 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 out 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 are driven off. S o w , t h e liquid is decanted through a n alundum crucible on a suction: and t h e residue is washed three times b y decantation with mater a t about 6 0 " C. The rubber substance is then transferred t o t h e crucible and washed ten more times with m-aim water, The residue is now placed in a tubel and dried in a stream of d r y carbon dioxide a t 100' C . for two t o four hours, The t u b e is t h e n remol-ed and allowed t o cool in a desiccator. The resulting residue is now transferred t o a v-eighing t u b e , from n-hick 0.3-g. samples are 1%-eighed for t h e final process, t h a t of combustion. The 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 and 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 a
20
< in inside diameter 1 The author uses a tube about 2 in. l o n g a n d with the lower third constricted to I in. inside diameter.
