THE INDIA RUBBER WORLD 



[September 1, 1917. 



What the Rubber Chemists Are Doing. 



THE PREPARATION OF RAW RUBBER. 



Till", preparation of raw rubber with special. rcTercnce to 

 "Slab" rubber and variability is discussed by B. J. Eaton 

 in the Agricultural Bulletin of the Federated Malay 

 States (February and March, 1917). The following questions 

 have been raised in connection with what has been termed liy 

 Eaton "Slab" rubber; that is, impressed, or lightly pressed or 

 rolled coagulum. 



/. Docs the preparation of this type of rubber lead to greater 

 variability or uniformity f Is it a solution of the problem of 

 uniformity^ 



In the opinion of the author llie preparation of this type of 

 rubber will tend toward greater uniformity than exists at 

 present. Putting aside the preparation of pale crepe, which may 

 be considered from the point of view of its uses a special 

 preparation, it is proposed to substitute "slab" rubber for sheet, 

 so that variability has to be considered, principally as between 

 slab and sheet. It has been shown that the cause of variability 

 in rate of cure is due chiefly to biological agencies, acting on 

 the protein constituents of the rubber, producing substances of 

 the nature of amines or amino acids which act as vulcanization 

 accelerators, and that numerous variable factors in methods 

 of preparation affect the amount of such accelerators which are 

 formed. It is obvious that the more variable factors the greater 

 the variability of the product. The author holds that greater 

 variability is introduced in sheet than in "slab" rubber, which 

 undergoes the minimum of handling. One of the greatest 

 factors responsible for variability in rate of cure of sheet rub- 

 ber is the rate of drying, including smoking, and, secondly, 

 the concentration of the latex and the amount of rolling. 



Since the primary cause of variability in rate of cure is 

 biological, it may be thought that considerable variability would 

 be caused by an uncontrolled fermentation or decomposition, 

 such as occurs in coagulum. It should be remembered that in 

 this country (Malaysia) the shade temperature is very constant 

 during the day and this constanc.v, in the author's opinion, is 

 responsible for the remarkable uniformity of the change which 

 takes place in unrolled coagulum left to mature for six days, 

 together with the fact that the latex during collection is thor- 

 oughly exposed to numerous chance organisms which enter it. 

 This remarkable uniformity of "slab" rubber has been proved by 

 the writer, not only in all his e.xperimental samples, which in- 

 clude many hundreds, but also in samples prepared on different 

 estates in various parts of the country. 



2. Is slab rubber, apart from the advantage to manufacturers 

 of its rapidity of cure, of better quality than other first-grade 

 types? 



All our experiments have shown that the tensile properties 

 of "slab" rubber are from 20 to 25 per cent better than those of 

 crepe rubbers and generally superior to sheet rubber, and since 

 sheet is superior to crepe in general, it may almost certainly be 

 argued that the keeping properties of vulcanized "slab" rubber 

 will also be superior. The superior tensile properties of "slab" 

 rubber may be either an inherent quality of the raw rubber, 

 or due to the much shorter time of vulcanization required for 

 its optimum cure and maximum tensile properties. 



There are thus two advantages in favor of "slab" rubber — 

 rapidity of cure and superior tensile properties. 



3. Will ultimate manufacturing difficulties be likely to be 

 greater than those which exist zvith present types of first latex 

 plantation rubber? 



There is absolutely no reason why the preparation of "slab" 

 rubber should cause greater confusion or difficulty for the manu- 

 facturer than is caused by the variability in rate of cure which 

 exists at present in the case of sheet and crepe rubbers. 



In demonstration tlic author cites the fact that a large Ameri- 

 can concern on its Malaysian plantation prepares "slab" rub- 

 ber for use in its own factories in .Xmcrica. 



4. In what form should slab rubber be shipped, hai-ing in view 

 the extra freight on wet rubber? 



There are only three forms in which "slab" rubber can be 

 placed on the market, as follows: (a) Virgin slab containing 

 about 20 per cent of moisture, (&) as dry crepe, (c) as block. 



The first form necessitates payment of freight on water to 

 practically the same extent as in the case of Fine Hard Para, 

 which does not appear to cause any difliculties on the market. 



The advantage of converting slab to crepe on the estate is 

 that freight on moisture is eliminated. It is doubtful whether 

 the advantage in favor of marketing this type of rubber in the 

 form of crepe is sufficient to neutralize the disadvantage of 

 shipping virgin "slab." 



Tlie third form in which this tyjic of rubber can be marketed 

 is dry block made from artificially dried crepe. At the present 

 stage no definite statement can be made as to which of the three 

 forms will eventually prove the most satisfactory, although in 

 the author's opinion, shipping in the form of virgin "slab" or 

 dried block is preferable to conversion to crepe on the estate 

 and shipping as crepe. 



The company referred to as shipping "slab" rubbers from its 

 estates packs it in bags only. 



The author expresses his opinion that the "slab" type of plan- 

 tation rubber is of considerably greater value than the types of 

 plantation Para rubber at present on the market and also is 

 superior to Fine Hard Para. 



GLYCERIN StTBSTITUTES. 



An efficient glycerol substitute by J. Lennox is reported as 

 follows in "Chemical Abstracts." Tlie formula yields a product 

 which has body, a sweetish taste and is reasonably permanent. 

 Irish moss (washed) 0.5 ounce; water, 24 fluid ounces. Keep 

 at boiling temperature in a covered vessel for IS minutes, strain 

 the mixture with pressure, pour upon the muslin boiling water, 

 make up to 19 fluid ounces ; then add glucose one ounce, mix 

 and strain through double ply without pressing. 



The drug trade is using a sugar syrup as a substitute for 

 glycerin. Its composition is invert sugar 46.8 per cent, sucrose 

 29.35 per cent, ash 0.05 per cent, water 23.8 per cent. This ma- 

 terial would probably be found valueless in connection with rub- 

 ber work where glycerin is employed. 



SUBSTITUTE FOR RUBBER. 



Sterilin is suggested as a substitute for rubber finger cots for 

 medical examinations. It fits the finger well, does not affect the 

 touch, is washable with soap, and can be disinfected with lysol 

 and corrosive sublimate. It cannot be sterilized in steam. [A. 

 Pinkus, Berlin, through "Chemical Abstracts."] 



ANTIMONY AS TRISULPHIDE. 



The following method for the determination of antimony as 

 trisulphide, by C. B. Clark, is based on the fact that antimony 

 trisulphide can be converted into the black crystalline modifica- 

 tion by passing hydrogen sulphide into the hot liquid containing 

 a large excess of hydrochloric acid. In practice the solution 

 of the antimony salt is heated with 24 to 1(X) cc. hydrochloric 

 acid on a w-ater bath, and frequently shaken while a current of 

 hydrogen sulphide is passed through it. The conversion of the 

 sulphide into the black form will be completed after 30 to 35 

 minutes. The precipitate is collected in a Gooch crucible, 

 washed with water and alcohol, and dried at 270 to 280 degrees- 

 C. in a current of carbon dioxide. 



