'2S 



THE INDIA RUBBER WORLD 



[August 1, 1920. 



The total rubber hydrocarbon is calculated by adding the 

 rubber hydrocarbon combined with the sulphur and the uncoin- 

 bined rubber hydrocarbon found from the bromine addition. 

 PROCEDURE FOR VULCANIZED RUBBER. 



Extract a weighed sample (appro.ximately 1.5 to 2.0 g.) of 

 vulcanized rubber with acetone for 8 hours in the standard 

 extraction apparatus, evaporating the acetone to obtain the per- 

 centage of acetone-soluble material.* Aspirate carbonic acid 

 through the rubber to remove the traces of acetone, reflux four 

 hours, with approximately 100 cc. of tetrachlorethane, cool, and 

 make up to mark in a 250-cc. calibrated flask with carbon tetra- 

 chloride. Remove a 2.S-cc. aliquot portion by applying gentle 

 suction to a pipette containing a small piece of cotton in its' tip. 

 Place this sample in a glass-stoppered bottle of 250 to 500 cc. 

 capacity, add from a burette a measured amount of bromine in 

 carbon tetrachloride corresponding to at least 100 per cent excess 

 bromine above that necessary for the addition reaction, insert 

 the stopper tightly, and allow to stand for three hours in a dark 

 closet. .At the end of this time, darken the room, add 10 cc. of 

 10 per cent potassium iodide solution, shake, and titrate rapidly 

 with 0.1 normal standard sodium thiosulphate, using starch paste 

 as an indicator. As soon as the first end-point has been noted, 

 add 10 cc. of 1 per cent potassium iodate solution, and titrate 

 rapidly to the second end-point with thiosulphate. The titration 

 of a blank run under similar conditions gives the thiosulphate 

 equivalent of the bromine added. 



The method of calculation of the results is entirely similar to 

 that used in the case of raw rubber, except that, to get total rub- 

 ber, the rubber equivalent to combined sulphur is added to that 

 determined by bromination. 



RESULTS. 



Table I — Rubber Hydrocarbon by Addition. 



Individual Runs. Per Cent. .\verage 



Sample. , — ^ ^ Per Cent. 



-■^ Sf.2 86.6 82.2 83.8 85.5 



B 63.5 66.5 .. 65.0 



C 56.6 52.6 52.7 50.7 53.2 



D 54.2 55.0 53.5 55.0 54.4 



E 45.4 452 .. .. 45.3 



F S0.5 .SI. 9 74.9 74.7 78.0 



The final analyses are summarized in Table II. 



og.S 



2.33 

 2.33 



Litliarge 



Zinc oxide 



Sublimed 



lead 



Mine) 

 rubber 



■§n:Sfl, ^.Seu ?< 



85.5 

 65.0 

 53.2 



Table II compares the percentages of total rubber hydrocarbon 

 as found by analysis with the known figures for rubber content 

 supplied by the compounders of the samples. In no case did the 

 analyst have any information as to the composition of the 

 samples. The analytical figures average low, as they should do, 

 because of the resin and protein content of the raw rubber. The 

 analytical results are, however, probably high for true rubber 

 hydrocarbon, because any sulphur combining with resin, protein, 

 or accelerator to give a product insoluble in acetone but soluble 

 in tetrachlorethane is figured over to its equivalent of rubber, 

 and, further, any sulphur substituting in rubber hydrocarbon 



*In case "factii 



itself will increase the results. These factors are probably neg- 

 Hgible, except for sulphur combined with artificial accelerators. 

 Any unsaturated organic material insoluble in acetone but dis- 

 solved by tetrachlorethane will also increase the analytical re- 

 sults. This is probably a cause of the high figures in the pres- 

 ence of mineral rubber. Few compounding materials are suffi- 

 ciently unsaturated, however, to be serious in this regard. 



It is believed that this procedure is by far the simplest and 

 most accurate direct estimation of the rubber content of vulcan- 

 ized articles. It should prove especially useful in the evaluation 

 of shoddies, because it shows the extent to which the unsatura- 

 tion of the rubber has disappeared,' due to previous vulcaniza- 

 tions. 



Within the experimental error, the results prove that rubber 

 hydrocarbon is unsaturated to an amount equivalent to four 

 atoms of bromine for each C,„H,e, and further that "combined" 

 sulphur reduces this unsaturation by two bromine atoms for 

 each sulphur combined. These facts seem incompatible with any 

 theory other than that the sulphur taken up by rubber on vul- 

 canization is chemically combined. 



£5,000 IN PRIZES FOR NEW USES OF RUBBER. 



THE Rubber Growers' Association, Inc., offers the following: 

 awards for ideas and suggestions for extending the present 

 uses or for encouraging new uses of rubber: <.nc prize of £1,000; 

 llircc prizes of £500 each; ten prizes of £100 each; a sum not 

 exceeding £1,500 to be divided among the remaining competitors 

 whose suggestions are considered to be of value, according to the 

 relative value of their suggestions, but so that no competitor will 

 receive more than £100. 



Suggestions must be practical and likely to increase the de- 

 mand for the raw^ material. Ideas will be welcomed for the 

 application in new directions of existing processes, methods or 

 manufactures, or for improvements or new processes which will 

 facilitate or cheapen the production of rubber goods. 



Competent judges (technical and otherwise) will be appointed 

 to investigate and adjudicate upon the suggestions received. 



-All competitors must accept the following conditions: 



CONDITIONS, 



suggestions of a thoroughly prac- 

 ictailcd information likely to make 



uggestions which are 



practical 



practical wilt 

 would absorb. 



requested bv 

 tion (at the 



Jbber Gi 



intend to make, and 



as disclosed by him 



no other person has 



patent (or like protec 



suggested by the con 



belief, the method, apparatus or process 



I'erson other than the competitor. 



4. The Council reserves the right 

 otherwise deal with suggestions mad. 

 receives a prize or not, in any manne 

 late the demand for raw rubber, and 

 have authorized such publication, tes 



or process suggested is to be protected in 

 or otherwise by the competitor or the Rubber 



successful competitor must be prepared, if 

 ers' .Association, to make a statutory declara- 

 sociation) that he has not made and does not 

 the best of his knowledge and belief, except 

 lance with clause 5 (f) of these conditions, 



intends to make, any application for letters 

 respect of the method, apparatus, or process 

 and that, to the best of his knowledge and 

 r process suggested is not the property of any 



by a 

 which 



time to publish, 



is thought likely 



petitors shall be d 



dealing with as 



5. Each suggestion to bear a kotk de flume or number, which should 



be placed upoi the right hand corner of each page used. Particulars should 



be clearly and legibly written or typewritten on one side of the paper only. 



In submitting suggestions competitors shall give the following particulars, 



with such others as they deem advisable: 



(o) A short preliminary descripticm of the suggestion, 

 (fr) As full a detailed description as possible shoaild follow, with 

 explanations, samples (if any), diagrams and designs to enable 

 the suggestions to be fully adiudicated upon by the judges and, if 

 necessary, adopted by .-i manufacturer. 

 (c) The facts upon which the competitor bases his belief in the value 

 ami practicahility of the idea, and his special means of knowledge 



