November 1, 1916.] 



THE INDIA RUBBER WORLD 



69 



Proceedings of the "Rubber Section'' — Continued. 



T'vo important addresses delivered before the Rubber Section of the American Chemical Society during the September, 1916, Con- 

 vention Zifere printed here last month. Below are given three other interesting papers. A full report of the symposium, in which 

 sofne 20 rubber chemists participated, mil be given in the December issue. 



WET COMBUSTION IN THE NITROSITE-COMBUS- 

 TION METHOD FOR THE DIRECT DETER- 

 MINATION OF RUBBER.* 



By L. C. Wesson and E. S. Knorr. 



IN order to make more feasible the possible use in technical 

 laboratories of the nitrosite combustion for the direct deter- 

 mination of rubber in rubber goods, we have attempted the 

 application of "combustion in the wet way" to this analytical 

 procedure. 



The "nitrosite-combustion" method as described in a previous 

 publication, is based upon the formation of the "nitrosite" of 

 rubber by the action of nitrogen oxide gases upon the caoutchouc 

 of th e sample. 

 This is then sepa- 

 rated from other 

 substances (fill- 

 ers), and burned 

 in a specially con- 

 structed electrical- 

 ly-heated combus- 

 tion tube. The 

 special apparatus 

 and technique re- 

 quired was a de- 

 cided obstacle to 

 the general use of 

 this method, even 

 should its reliabil- 

 ity be demonstrat- 

 ed, and we there- 

 f o r e turned to 

 "wet combustion" 

 as an escape from 

 this difficulty. 



In the course of 

 our experiments, 

 acetone - extracted 



crude rubber was first used. The nitrosite was formed in the 

 flask used for the combustion, and after the complete expulsion 

 of the rubber solvent (chloroform), the comlnistion followed in a 

 manner quite similar to those later described. We obtained as 

 dependable values, 96.8, 97.0, 97.6 and 97.1 per cent C,o H,„. Aver- 

 age is 97.1 per cent; theoretical, 97.3 per cent C,„ H,,,. 



In tlie regular analytical procedure this simple treatment of 

 the nitrosite is not possible, since the latter must be separated 

 from the mineral matter and other impurities by the use of some 

 solvent, after filtration from the chloroform. We first used as 

 solvent, acetone, which was added to the dry nitrosite in the 

 combustion flask. The acetone was first evaporated off, then 

 the flask was heated 1 1/2 hours by a boiling water bath whilst 

 a current of dry air passed slowly throusb the flask. The value 

 now obtained, (100.7 per cent) upon combustion, indicated a re- 

 tention of acetone. 



A repetition of this experiment vvitli the use of only ethyl ace- 

 tate as solvent gave 96.4, 97.1 and 97.0 per cent C„, H,„. These 

 figures were more promising. Moreover, the ethyl acetate on 

 evaporation left the residual nitrosite in a more porous, and thus 



G. Wesmi.x. 



more favorable condition for rapid expulsion of the organic sol- 

 vent than did the acetone. Ethyl acetate was therefore adopted 

 as the solvent in all of the analyses of vulcanized rubber. 



The use of acetic ester did not, however, eliminate our troubles 

 with retained solvent, as we found when we next turned to the 

 analysis of compounded rubber samples, instead of the raw gum. 

 We believe that this difficulty explains most of the erratic results 

 we had to the end of our work. We believe that we have now 

 found the remedy for this retention of solvent in the addition 

 of water, containing a drop of hydrochloric acid, to the nitro- 

 site, and subsequent evaporation of this to dryness, after all 

 solvent has been removed in the ordinary way. 



In a sample compounded with 35.0 per cent Fine Para, using 



the method de- 

 scribed, we found 



34.7, 34.9, 34.8 and 

 34.2 per cent CjoH,,. 

 Average is 

 34.7 per cent; the- 

 oretical. 34.4 per 

 cent C,„ H,e. 



In a sample 

 compounded with 

 40.0 per cent 

 plantation rubber, 

 ■we f o u n d 38.9, 



39.8. 37.9, 38.1 and 

 37.7 per cent Qo 

 His. The average 

 is 38.5 per cent, 

 and tlie tlieoret- 

 ical value is 38.3 

 per cent C]„ H,c.* 

 THE PROCEDURE. 



Prep.\ration of 

 THE Nitrosite for 

 E. S. Knorr. the Combustion. 



After the rubber 

 sample has been ground in a meat-chopper to pass a 20- 

 mesh sieve, and 1/2 gram of it extracted 3 hours with acetone, 

 and 1/2 hour or longer with chloroform, the extracted sample is 

 allowed to dissolve in, or thoroughly absorb chloroform. A small 

 Florence flask (75 cc. ) is used, which may be about one-half full 

 of the solvent. Nitrous oxide vapors, evolved from dilute nitric 

 acid (specific gravity 1.3) and arsenic trioxide, are then passed 

 through the cooled chloroform until the deep green color becomes 

 permanent for, say, 15 minutes, and the whole allowed to stand 

 over night for completion of the action. 



The chloroform is then decanted through a dry Gooch crucible 

 and asbestos matte (the former rests in an ordinary 60 degree 

 filter funnel) into the combustion flask, from which the chloro- 

 form is then evaporated by means of a boiling water bath and 

 a dry air current.f Meanwhile the residue in the Florence flask 

 has been similarly dried. The separation of fillers and nitrosite 

 is now brought about in the following way. Small portions 

 (5 cc.) of calcium chloride-dried ethyl acetate are added to the 

 residue in the Florence flask, the latter warmed, and the liquid 



•The article here published represents thesis work dune hy one of us 

 (E. S. Knorr) in the course for the degree of Bachelor of .Science in 

 Chemistry from the Case School of Applied Science. 



*These .sampiss were kindly sent us by the Bureau of Standards. 



tj. B. Tultle, of the Bureau of .Standards, has found that the chloroform- 

 soluble residue thus recovered may be very appreciable, and it is to his 

 sugKestion that this modification is due. 



