112 PARA. RUBBER. 



Method of determining the Amount or Acetic Acid required. 



It has been contended that many inventions which have recently 

 been brought forward necessitate dilution, to varying degrees, with 

 water, ammonia, and formalin, and that such dilution prevents 

 the planter from knowing how much latex the coolies collect, and 

 how much acetic acid will be required in the process of coagulation. 

 It is quite true that the latex so treated will contain varying quanti- 

 ties of rubber, but when one considers the variation in composition 

 of ordinary samples of undiluted latex from different trees, or when 

 obtained at different times of the year from the same trees, it is 

 obvious that the same difficulty has ordinarily to be overcome ; the 

 objection is, therefore, not a very serious one so long as latex is not sold 

 by volume. 



The application of the same quantity of acetic acid to the same 

 volume of latex cannot be recommended except for expediency. The 

 acid should be added in order to neutralize or faintly acidify the 

 latex, and it is better to determine the exact quantity required 

 rather than add too much. 



The amount of acid required can be determined with ease. Let 

 the coolies pour the diluted latex from the different trees into a set- 

 tling tank or ordinary receptacle and fill up to a known level, so that 

 the exact volume will be known. After thoroughly stirring the mix- 

 ture take a small sample of known volume and add dilute acetic 

 acid of constant strength , drop by drop, from a burrette or graduated 

 glass tube, until the whole mixture after stirring is neutral or faintly 

 acid. On measuring the volume of acetic acid used, the amount 

 required for complete coagulation of the latex in the settling tank 

 can be easily calculated and added. Litmus paper can be used to 

 determine when sufficient acetic acid has been used ; the resultant 

 solution should be only faintly acid or neutral, blue litmus paper 

 becoming faintly red and red litmus paper remaining unchanged 

 respectively in such solutions. 



Such a method involves the accumulation of the latex in recep- 

 tacles of known capacity and provided with mechanical means for 

 keeping the latex in a liquid state. Some such apparatus may or may 

 not be required as the trees on the various rubber estates are more 

 frequently tapped. 



Advantages and Disadvantages of adding Chemicals to the 

 Latex. 

 It has been frequently contended that the home manufacturers 

 object to the use of chemicals in the coagulation of the latex, parti- 

 cularly mineral and vegetable acids, on account of the fact that even 

 after thorough washing and pressing some of the acid may still re- 

 main in the rubber and subsequently prove harmful in the manu- 

 facturing processes. The retention of a large proportion of foreign 

 chemical ingredients is said to lead to the production of bubbles and 

 blow holes and to be occasionally accompanied by early deterioration 

 of the prepared rubber. 



