PARA RUBBER. 113 



On the other hand, it can be shown that the addition of reagents 

 such as formalin, corrosive sublimate, creosote, or acids such as for- 

 mic or even hydrofluoric , have a preservative effect on the rubber 

 when used in infinitely small quantities. When one considers the 

 chemicals which are incorporated in rubber of good repute prepared 

 by the natives in the Amazon district and the inert characteristic of 

 rubber itself, the objection to the use of minimum quantities of re- 

 agents such as acetic acid and creosote seems to be less tenable. But 

 apart from the preservative action of some of the chemicals used, 

 there is a much more serious advantage, to the producer, accompany- 

 ing the use of the required quantity of acetic acid, viz. , the rapidity 

 and completeness of the coagulation effected. 



In one experiment about 1£ gallon of ordinary latex was poured 

 into a large glass beaker and allowed to coagulate naturally. At the 

 end of two days a large cake of rubber had formed at the top of the 

 liquid, but the mother liquor was still quite milky ; the cake of rubber 

 was removed, and subsequently thinner cakes appeared at the sur- 

 face and were removed; after six days the mother liquor still remained 

 turbid, and a further quantity of rubber was prepared from it by 

 treatment with a small quantity of acetic acid and heating. The 

 completeness of coagulation, when the latex is allowed to set un- 

 treated with acids, does not always take such a long time, but it is 

 probable that the same phenomenon may repeat itself, and thus 

 necessitate considerable delay and perhaps waste ; certainly it would 

 involve considerable irregularity to the producer. The use of acetic 

 acid, on the other hand, effects coagulation in a few hours, and the 

 mother liquor becomes perfectly clear in less than a day ; the pre- 

 cipitation is complete, and there is therefore no waste of rubber. 



If the producer is compelled to cease using acetic acid for assisting 

 coagulation, and has to produce his rubber by simply allowing the 

 latex to slowly ferment, there are other difficulties in the way. It is 

 obviously to the advantage of the producer to reduce the proportion 

 of scrap in his rubber and to keep the latex flowing as long as possible, 

 and the use of ammonia and formalin to accomplish this is being 

 adopted on many estates during tapping operations ; the presence 

 of these reagents in the latex tends to prevent coagulation, and they 

 would, therefore, further aggravate the question of delay necessary if 

 the natural process of coagulation were compulsory ; a longer period 

 of time would be required for the necessary acidity to develop in 

 presence of either of these reagents. 



In the absence of definite information from home manufacturers, 

 the use of minimum quantities of acetic acid, determined by the 

 simple method previously described, is likely to be continued by the 

 producer in the Tropics, and is an essential point in the preparation 

 of fine Para rubber in Brazil ; it will be necessary to prove that the 

 effect of the use of acetic acid is really bad before the producer will 

 risk the possible loss in yield suggested by the frequent turbidity 

 of the mother liquor, and the uncertainty or delay incurred in the 

 production of rubber from latex by the natural process. 



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