July, 1920
T H E J O U R N A L OF 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
673
scribed previously. It will be noted t h a t results for A DIRECT METHOD FOR THE DETERMlNATION OF RUBBER HYDROCARBON IN RAW AND Samples 3, 4, and j are slightly better when using VULCANIZED RUBBER‘ 0.8517 g. t h a n when using 1.7034 g. It was also found By W. I(.Lewis and W. H. McAdams from results not reported, using Sample 5, t h a t using MAS3ACHu1.7034 g. sample with 5 0 cc. salicyl-sulfonic acid DSPARTMENTOF CHEMISTRY AND CHEMICAL ENGINEERING, SETTS INSTITUTE OF TECHNOLOGY. CAMBRIDGE, MASS. (containing 1.5 g. salicylic acid), j g. hypo, 5 t o 6 g. I n t h e fall of 1916 t h e writers noticed in t h e literapotassium sulfate, I g. mercury, 2 g. sodium sulfide, etc., t h a t t h e same results were obtained as when using ture* a number of articles concerning analytical methods 0.8517 g . with 3 5 cc. of acid, etc. Here again the for the determination of rubber hydrocarbon in raw proportions of reagents and sample are found t o be and vulcanized rubber, depending upon the bromine important and indicate t h a t for samples containing absorbed by rubber. A survey of these articles showed high nitrate content, say, 4 per cent ammonia or over, t h a t several different types of bromination methods more correct results may be obtained by using 0.8517 had been proposed, but t h e results appeared t o be very g. sample, as the use of 50 cc. of acid is hardly t o be discrepant. The most promising type seemed t o be t h e one involving t h e addition of a known amount of recommended. Determinations were also made on Samples 2, 3, 4, bromine, dissolved in a suitable organic solvent, such and 5 by warming after adding the salicyl-sulfonic as carbon tetrachloride, t o a solution of t h e rubber in acid, as described before in case of nitrate, but for all an organic solvent. After the solution had stood for samples t h e results were slightly lower, amounting a period of time t h e unabsorbed or excess bromine was determined by titration, usually by the addition from 0.05 per cent t o 0.10 per cent ammonia. of standard sodium thiosulfate in the presence of K I SUMMARY solution and starch paste. From t h e foregoing i t appears t h a t the best and Inasmuch as this paper will not deal with t h e strucreally most convenient procedure for t h e determina- tural formula of rubber, t h e conventional formula tion of total ammonia in fertilizers containing nitrate (CIoH16)1Z will be used t o designate rubber hydrocarbon, is as follows: with the understanding t h a t this contains 212 double Weigh 1,7034 g. sample (0.8517 g. in case of mixtures bonds. Two types of reaction are possible, involving high in nitrate) preferably into a 6 j o cc. Pyrex Kjel- in t h e first case, addition, and in the second, substitudah1 flask, add 3 j cc. salicyl-sulfonic acid, containing tion, of bromine. I g. salicylic acid, and after shakiing frequently for I j min. add 5 g. hypo, heat gently until frothing ceases, add 5 g. potassium or sodium sulfate, 0.5 g. mercury, and digest until clear and for 1.5 hrs. or more after- I n the second reaction it will be noted t h a t two atoms wards, cool, dilute t o about 400 cc. and proceed as in case of bromine are necessary t o substitute one atom of hydrogen, thereby producing one formula weight of of nitrate samples, using in this case I g. sodium sulfide. Altogether over I ,000 determinations have been HBr. Some of t h e investigators found t h a t substitumade on nitrate samples and about zoo determinations tion occurred, and tried t o choose conditions such t h a t on t h e four mixed fertilizer samples and t h e results substitution would be minimized or entirely prevented. McIlhiney3 has shown t h a t in the bromination of summarized in t h e foregoing tables. All determinations have been corrected for ammonia in reagents, by unsaturated oils in an organic solvent the bromine blank determinations run with nearly every set, not only adds t o the double bonds as in Reaction I measuring apparatus carefully calibrated, standard b u t a considerable amount is substituted as in Reacsolutions frequently checked and allowance made for tion 2 . Gill4 states t h a t rosin oil shows a very high change in temperature of these solutions. The 0.5 N substitution. This paper deals with t h e application of t h e Mcsulfuric acid solution was standardized by three methods: (I) By sodium carbonate prepared as per Ilhiney method, developed for unsaturated oils, t o Scott,’ ( 2 ) b y acid potassium phthalate prepared and rubber hydrocarbon. Briefly, it consists in determinused as described by Dodge,2 and (3) by determination ing b y a volumetric method t h e substitution which as barium sulfate, cold precipitation method of Allen does occur under t h e particular conditions of the and Bishop. The results by the three methods of analysis in question, and deducting twice the observed standardizing agreed closely, and were as follows in substitution from t h e bromine consumed, which gives order named: 100.20 per cent, 100.13 per cent, and a measure of t h e true bromine addition, from which t h e rubber hydrocarbon is readily calculated. 1.00.17 per cent 0.2 N , average 100.17 per cent. The writer hopes t h a t this contribution t o the literaEXPERIMENTAL PART-RAW RUBBER ture for t h e correct valuation of nitrate and the deter’ PREPARATION O F P U R E RUBBER HYDROCARBON S O L U mination of total nitrogen in samples of fertilizer con- TIow-Plantation pale crepe was extracted overnight taining nitrate may be of value t o others and serve in with acetone5 in t h e standard extraction apparatus some measure toward the adoption of more uniform 1 Read before the Rubber Division at the St. Louis Meeting, American methods of analysis; also t h a t t h e West Coast method Chemical Society, April 12-16, 1920. 2 See Bibliography, p. 676. for valuation of commercial nitrate of soda may be 3. A m . Chem. SOC.,21 (1899). 1084. relegated t o the obsolete. 4 “Oil Analysis,” 9th Ed. (Revised), p 67. I toc.
cit.
*THISJOURNAL, 7 (1915). 29.
6 The acetone was allowed to stand with NanCOa and CaClz and then fractionally distilled.
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T H E J O U R N A L OF 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
to remove the resins, then carefully dried, dissolved in pure carbon tetrachloride, and finally filtered t o remove the proteins and other insoluble matter. The resulting solution of pure rubber hydrocarbon was analyzed by evaporation t o determine the total solids present in a known volume, and this known rubber hydrocarbon content was used as’ a basis of comparison with the calculated figures found by bromine addition as described below. PROCEDURE-TOa known volume of t h e above pure rubber hydrocarbon solution, containing approximeasured )~, volume of bromine mately 0 . 2 g. ( C ~ O H a~ ~ in pure carbon tetrachloride corresponding t o approximately I jo per cent excess bromine above t h a t necessary for addition was added, and the mixture was allowed to stand in glass-stoppered bottles for varying lengths of time in a dark closet a t room temperature. After this exposure t o bromination, I O cc. of a 3 per cent K I solution were added to take up t h e excess bromine, and the resulting iodine was titrated by means of 0 . 2 j N standard sodium thiosulfate, using starch paste as an indicator. I n order t o determine the substitution which had occurred, I O cc. of 5 per cent K I 0 3 were now added t o convert t h e equivalent of the HBr into iodine, which was then titrated t o a second end-point. A blank was run under the same conditions as the rubber determination in order t o determine the bromine added t o the rubber analysis, and to eliminate any error caused by impurities in t h e reagents used. The sample calculation given below indicates the relation of the various readings.
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One possible objection t o this method is t h a t substitution might continue after the addition of t h e K I solution. It will be noted t h a t after this time no halogen except iodine is present in the solution, and iodine is known t o be much less apt t o substitute hydrogen t h a n bromine.. Furthermore, if iodine substitution during titration took place before the first end-point no error whatever would be introduced; the effect would be the same as if bromine had been substituted, as the H I so formed would be determined in the second titration and hence a n automatic correction would be introduced for this action. However, if iodine substitution took place after the first endpoint (by the substitution of iodine produced by the action of KIO, on the H I already present) the second titration would be high and the calculated addition would be low, because the addition is obtained by subtracting twice the second titration from the bromine consumed in t h e first. Furthermore, if at any time HBr splits off from t h e brominated molecule and this action is not accompanied by further addition, the calculated addition would be low. The results as shown in the attached plot indicate t h a t if such undesirable actions occurred they were negligible in effect.
Rubber taken = 0.2000 G . Thiosulfate Solution = 0.235 N Equivalent Weight of Rubber Hydrocarbon, (CiaHia), = 34 Cc. Thio Forblank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70.00 Excess found by first titration.. ......................... 38.00 Consumed ............................................ 32.00 7.00 Twice second titration, (2) (3.5) ........................ True addition.. ....................................... 25 .OO 25’00 0.2000 34 x0’235 loo = 100 per cent theoretical addition 1000
N0TEs-h order t o avoid loss of bromine vapor upon opening the bottle after the bromination period, t h e bottle was cooled by immersion for a few minutes in ice water, in the dark, and the K I solution was introduced by means of I-in. rubber tubing attached t o the neck of the bottle and extending up above t h e stopper. The carbon tetrachloride was purified by subjecting i t t o t h e action of saturated chlorine water for several days in diffused daylight, followed by washing with water and drying with CaO, previous t o a distillation in which t h e fraction boiling within I O C. of the proper boiling point was taken. DISCUSSION OF RESULTS-The attached plot shows typical results’ of runs on extracted, filtered pale crbpe. It will be noticed t h a t the substitution increased with t h e bromination time, but t h a t t h e addition followed closely the theoretical I O O per cent line, when the time of exposure was 2 t o 4 hrs. The substitution is doubtless a function of t h e conditions under which the experiment is conducted. For example, i t is quite possible t h a t a small amount of water present during t h e bromination would increase the substitution. Brandegee, 1917. Thesis submitted in partial fulfillment of the requirements for the S.B. degree at the Massachusetts Institute of Technology. 1
Substitution
0‘
I 2
I
I
4
6
Hou r 5
I
- 1
8
IO
12
I
I4
I
16
VULCANIZED R U B B E R
The above results have shown the method t o be satisfactory for raw rubber; i t remained for Sackett and Seltzer’ t o adapt i t t o vulcanized rubber. Since carbon tetrachloride will not “dissolve” vulcanized rubber, a new “solvent” had t o be obtained, and t h e choice was tetrachlorethane. I n addition t o t h e rubber hydrocarbon, resins, a n d proteins present in raw rubber, vulcanized rubber may contain fillers and compounding materials, such as mineral oxides or salts, carbon, mineral rubber, organic accelerators, vulcanized oils (factice), free sulfur, a n d sulfur combined as polyprene disulfide, (CIOHI~S~)~. The acetone extraction of t h e finely cut sample was made t o remove not only resins but also free 1 Sackett and Seltzer, 1918. Thesis submitted in partial fulfillment of the requirements for the S.B. degree a t the Massachusetts Institute of Technology.
July,
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
1920
sulfur and other acetone-soluble materials. The rubber residue was dissolved by refluxing with tetrachlorethane1 for several hours, diluted t o a definite volume with carbon tetrachloride, and allowed t o settle, then an aliquot part was pipetted out for bromination as in Brandegee’s method. The finely divided fillers were excluded from t h e aliquot part so taken by placing a wad of cotton in the tip of the pipette, and applying a gentle suction. By this means t h e troublesome centrifuging procedure for eliminating solid material was avoided. During the course of the experimental work Sackett and Seltzer found t h a t substitution could be reduced practically t o zero by titrating t h e brominated sample in very dim daylight, thus eliminating a difficulty previously met by them in an unstable end-point during t h e second titration. When t h e per cent excess bromine above t h a t necessary for addition was small (50 per cent) t h e results were low; I O O t o 1 5 0 per cent excess bromine gave t h e best results. C O M B I N E D S U L F U R PROCEDURE-The combined sulfur was found by evaporating t o dryness in a porcelain casserole an aliquot part of t h e tetrachlorethane solution free from insoluble matter, and determining the sulfur by t h e method of Daviese2 This consisted in adding I O cc. of saturated arsenic acid solution, I O cc. of fuming nitric acid, and 3 cc. of bromine water, and evaporating t o a sirupy consistency. (If all the organic matter is not destroyed, more fuming nitric acid is added, and the mixture again evaporated t o a sirupy consistency.) After t h e addition of a few crystals of potassium chlorate, t h e solution is evaporated t o dryness, heated to boiling with 50 cc. of I O per cent hydrochloric acid solution, filtered through paper, and diluted t o 300 cc. with distilled water in a beaker. The sulfuric acid is precipitated as barium sulfate by t h e addition of barium chloride, and determined gravimetrically in t h e usual manner. CALCULATION
OF
TOTAL
RUBBER
suction t o a pipette containing a small piece of cotton in its tip. Place this sample in a glass-stoppered bottle of 2 5 0 t o 500 cc. capacity, add from a burette a measured amount of bromine in carbon tetrachloride corresponding t o at least I O O per cent excess bromine above t h a t necessary for the addition reaction, insert the stopper tightly, and allow t o stand for 3 hrs. in a dark closet. At the end of this time, darken the room, add I O cc. of I O per cent K I solution, shake, and titrate rapidly with 0.1 N standard sodium thiosulfate, using starch paste as an indicator. As soon as the first end-point has been noted, add I O cc. of I per cent KIOI solution, and titrate rapidly t o the second endpoint with thiosulfate. The titration of a blank run under similar conditions gives the thiosulfate equivalent of t h e bromine added. The method of calculation of the results is entirely similar t o t h a t used in t h e case of raw rubber, except t h a t to get total rubber the rubber equivalent t o combined sulfur is added t o t h a t determined by bromination. _I
RESULTS TABLEI-RUBBER HYDROCARBON B Y ADDITION INDIVIDUAL RUNS AVERAGE SAMPLE PER CENT PBR CENT A , . . . . . . . . . . . . . . 8. 6 . 2 86.6 86.2 83.8 85.5 B . . . . . . . . . . . . . . . . 63.5 66.5 65.0 C _ . . . . . . . . . . _ . . .5.6 . 6 52.6 5i:7 5017 53.2 D .... , , . . , , , , . , 5 4 . 2 55.0 53.5 55.0 54.4 45.3 E . . . . . . . . . . . . . . 4. 5. . 4 45.2 F. . . . . . . . . . . . . . . . . 8 0 . 5 81.9 74:9 7417 78.0
.
.
The final analyses are summarized in Table 11. TABLEXI Rubber EquivaCorn- lent of Nature bined ComAcetone of Corn- Sul- bined Extract pounding fur Sulfur Per MaPer Per Sample cent terial cent cent A 3.46 None 3 . 4 7.2 B 1 . 9 0 Litharge 3 . 1 6.6 C 2 . 3 3 Zincoxide 3 . 3 7.0 D 2 . 3 3 Sublimed lead 1.6 3.5 E . Zinc oxide
.
F
,
UncomError bined -Total in Rubber Rubber Total (by Total Known Rubber Bromi- Rubber Corn- Hydronation) (by position carbon Per Analysis) Per Per cent Per cent cent cent 85.5 92.7 9 3 . 7 -1.05 65.0 71.6 75 -3.4 53.2 60.2 60 4-0.2 54.4
57.9
60
-2.1
2.4
45.3
47.7
48
-0.4
4.6
78.0
82.6
80.5
4-2.1
and or~~~.~
HYDROCARBON-
The rubber hydrocarbon combined with t h e sulfur thus found is calculated by multiplying the percentage C i o H i ~ 136 of sulfur by -, o r - = 2.13.
675
.
ganic accelerator 1 . 1 Mineral rubber and accelerator 2 . 1 6
Table I1 compares the percentages of total rubber hydrocarbon as found by analysis with the known The total rubber hydrocarbon is calculated b y adding figures for rubber content supplied by t h e compounders the rubber hydrocarbon combined with the sulfur of t h e samples. I n no case did t h e analyst have any and t h e uncombined rubber hydrocarbon found from information as t o t h e composition of t h e samples. t h e bromine addition. The analytical figures average low, as they should do P R O C E D U R E F O R V U L C A N I Z E D RUBBER-Extract a because of the resin and protein content of t h e raw weighed sample (approximately 1 . j t o 2 . 0 g.) of vulrubber. The analytical results are, however, probably canized rubber with acetone for 8 hrs. in t h e standard high for true rubber hydrocarbon, because any sulfur extraction apparatus, evaporating t h e acetone t o combining with resin, protein, or accelerator t o give a obtain t h e percentage of acetone-soluble material3 product insoluble in acetone but soluble in tetrachlorAspirate Cor through t h e rubber t o remove the traces ethane is figured over t o its equivalent of rubber, and, of acetone, reflux 4 hrs. with approximately I O O cc. further, any sulfur substituting in rubber hydrocarbon of tetrachlorethane, cool, and make up t o mark in a itself will increase the results. These factors are 250 cc. calibrated flask with carbon tetrachloride. probably negligible, except for sulfur combined with Remove a 2 5 cc. aliquot portion by applying gentle artificial accelerators. Any unsaturated organic ma1 This solvent was purified in the same manner as the carbon tetra. terial insoluble in acetone b u t dissolved by tetrachlorchloride. * Chemist-Analyst, 15 (1915), 4. ethane will also increase the analytical results. This 8 In case “factice” (vulcanized oil) is present, it should be removed of t h e high figures in t h e presence is probably a by treatment in the usual manner by extraction with alcoholic potash. of mineral rubber. Few compounding materials are This treatment was unnecessary for the samples used. SZ
64
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T H E J O U R N A L OF 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
sufficiently unsaturated, however, t o be serious in this regard. I t is believed t h a t this procedure is by far t h e simplest and most accurate direct estimation of t h e rubber content of vulcanized articles. It should prove especially useful in t h e evaluation of shoddies, because i t shows t h e extent t o which t h e unsaturation of t h e rubber has disappeared, due t o previous vulcanizations. Within t h e experimental error, t h e results prove t h a t rubber hydrocarbon is unsaturated t o a n amount equivalent t o four atoms of bromine for each CI0H16, a n d further t h a t “combined” sulfur reduces this unsaturation by two bromine atoms for each sulfur combined. These facts seem incompatible with any theory other t h a n t h a t t h e sulfur taken up b y rubber o n vulcanization is chemically combined. SUMMARY
I-Working with a filtered carbon tetrachloride solution of acetone-extracted plantation pale cr&pe, i t has been shown b y a volumetric method involving a double titration t h a t t h e bromine consumption, corrected for t h e observed substitution, is a true measure of t h e actual amount of pure rubber hydrocarbon known t o be present. Although t h e amount of substitution increases with t h e length of t h e bromination period, t h e addition corresponds quantitatively t o t h e actual amount of pure rubber hydrocarbon present, when t h e bromination time is from 2 t o 4 hrs. 11-Experimental d a t a are given t o show t h a t t h e actual per cent of (C10H16)~in vulcanized soft rubber can be determined by a volumetric bromination method herein described, involving a second titration t o correct for t h e substitution which accompanies t h e particular analysis; by titrating in dim daylight, this substitution correction can be made very small. 111-Tetrachlorethane is a suitable “solvent” for t h e soft vulcanized rubber goods used. IV-Experimental d a t a shows t h a t t h e so-called “combined sulfur” in soft vulcanized rubber is actually combined with t h e double bonds of t h e rubber hydrocarbon. ACKNOWLEDGMENT
The writers desire t o express their appreciation of t h e cooperation of t h e Chemical Department of t h e Goodyear Tire & Rubber Company, in preparing samples of known rubber content, and their indebtedness t o Messrs. Brandegee, Sackett and Seltzer for developing the analytical procedures and making most of t h e analyses. BIBLIOGRAPHY Gladstone and Hibbert, “The Optical and Chemical Properties of Caoutchouc,” Trans. Chem. S a c , S3 (1885), 679. T h Budde, “The Valuation of Cold Vulcanized Rubber Ware by the Tetrabromide Method,” Chem. A b s . , S (1909). 3013. P.Schidrowitz, Rubber, London, ‘1911. C. 0. Weber, “The Chemistry of India Rubber,” London, 1939. Hinrichsen, Quensell and Kindscher, “The Chemistry of India Rubber. 111-Addition Compounds of Hydrogen Halides and Halogens with Rubber,” Chem. A b s . , 1(1913), 2482. Hinrichsen and Kindscher, “Direct Determination of Caoutchouc as Tetrabromide,” Chem. Abs., 7 (1913), 2861. Caspari, “India Rubber Laboratory Practice,” London, 1914 W. A Ducca, “Testin; Methods of Rubber Content in Raw and Vulcanized Rubbers,” THISJOURNAL, 4 (19111, 372. Utz, “The Determination of Rubber as Tetrabromide,” Chem. A b s . , 0 (1912). 2009.
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D. Spence and J. C. Galletly, “The Determination of Caoutchouc a s Tetrabromide,” Chem. Abs., 6 (1912), 302. E Kirchhof, “Direct Determination of Rubber by Titration with Bromine,” Chem. Abs. 7 (1913), 270. G. Huebner, “Analyses and Analytical Methods for Hard Vulcanized Rubber,” Chebz. A b s . , S (1909), 1697. G. Huebner. “Method for Determining Rubber in Hot Vulcanized, Soft Rubber Goods,” Chem. Abs., 3 (1909), 2388. G. Huebner, “The Direct Determination of Rubber in Vulcanized Rubber Wares,” Chem. A b s . 6 (1911), 3172. Caspari. “Bromination of Vulcanized Rubber,” Chem. Abs., 6 (1912), 162. W. Esch, “The Analysis of Vulcanized Rubber by the Bromine Method,” Chem. Abs., 6 (1912), 806. T. Budde, “A New Method of Determining the Combined Sulfur in Vulcanized Rubber,” Chem. Abs., 3 (1909), 1936. W. Vaubel, “Contribution t o the Bromide Method for the Determination of Rubber,” Chem. Abs., 7 (1913), 275. W. Schmitz, “The Direct Volumetric Estimation of Rubber by Bromine, Chem. Abs., 7 (1913), 4084. G. Fendler and 0. Kuhn, “New Researches on Rubber,” Chetn. Abs., 2 (1908), 593. G. Huebner, “Concerning Hard Vulcanized Rubber,” Chem. Abs., 4 (1910), 1550. B D. Porritt, “The Chemistry of Rubber,” Chemical Monograph, No. 111, New York. (Many articles discussing methods, including minor modifications of the same, proposed by the above writers have been omitted from this list.)
METHOD FOR THE DETERMINATION OF THIOCYANATES IN AMMONIACAL LIQUOR AND WASTE LIQUOR FROM AMMONIA STILLS IN THE BY-PRODUCT COKING INDUSTRY By Joseph A. Shaw €COPPERSCOMPANY LABORATORIES, PITTSBURGH, PA. Received January 8, 1920
T o 5 0 0 cc. of ammoniacal liquor are added 3 to 5 g. of ferrous sulfate in water solution and about I O O cc. of a I O per cent sodium hydroxide solution. This is stirred thoroughly and allowed t o stand overnight. It is then filtered with gentle suction and washed with cold water containing about 30 g. of sodium hydroxide per liter. The long standing in alkaline solution is necessary in order t h a t t h e insoluble organic matter may be removed thoroughly from t h e solution. If this is not done i t will continue to settle out from time t o time and is liable t o cause t h e analyst to be doubtful of t h e sharpness of some of his reacti0ns.l By this procedure organic and inorganic material insoluble in alkalies and t h e sulfides have been removed from t h e sample and the cyanides changed t o ferrocyanides. The alkaline solution is heated t o 60’ C., made slightly acid with dilute sulfuric acid, and the ferrocyanides precipitated with a slight excess of a I O per cent ferric chloride solution. After standing a short time t h e Prussian blue, together with a considerable sludge insoluble in acid solution, is filtered off on a filter similar t o t h e one used t o filter the sulfide sludge. The residue may be used t o cletermine total cyanogen after having been washed with a 5 per cent solution of sulfuric acid containing 5 per cent by weight of sodium sulfate. The filtrate is now made t o a definite volume and 1 It is necessary t o use a special filter for the removal of the sludge from the solution mentioned above. This filter is made by placing a perforated porcelain plate in a funnel attached t o a filter flask and covering it with a piece of oversized filter paper. When this is drawn into place by the suction a thin layer of asbestos pulp is poured on the filter and another piece of filter paper cut considerably under size is placed on top. After a little washing and adjustment the filter is ready to use. Or if desired and available a small Btichner funnel may be used instead of the funnel and porcelain plate employed above.
