130 PARA RUBBER. 



depend upon the percentage of albuminous matter present in 

 the latex to be acted upon. Whilst the latex is in an alkaline 

 condition the albumen remains soluble, but it is only necessary 

 to neutralise or slightly acidify the latex to render it insoluble. 

 The exact amount of acid to apply may be ascertained by test- 

 ing with litmus paper. When the latex is in a neutral condition 

 litmus paper will neither be turned red nor blue ; immediately 

 acidity is formed the latter will turn red. It is important to bear 

 in mind, however, that in the addition of too much acid there 

 is a danger of re-dissolving the proteids, thus retarding coagula- 

 tion. Here again the putrescible matters remain in the rubber. 



It has been shown that in the manufacture of crepe rubber a 

 certain amount of them are washed away, but no mechanical 

 means exist for the extraction of the whole from coagulated 

 rubber. 



The use of centrifugal machines has been suggested for 

 separating the caoutchouc globules free from proteids, resins, &c., 

 in a similar way to that employed for treating animal milk, but 

 Wright states : " It is very difficult to separate the caoutchouc by 

 centrifugal force, and on several occasions a speed of 10,000 

 revolutions per minute did not effect a separation of the 

 caoutchouc of normal latex." 



The proteids may be kept quiescent in Para latex by adding 

 some antiseptic substance, such as creosote, or corrosive subli- 

 mate, i.e., bichloride of mercury. 



Creosote does not mix readily with latex, .but if first diluted 

 with alcohol in the proportion of ten parts alcohol to one of 

 creosote the process is simplified. Biscuits prepared by Parkin 

 from Hevea latex with creosote and acetic acid had not lost any 

 of their tensile strength nor appeared to have deteriorated in 

 any way eight years later. 



It was suggested at the Ceylon Rubber Exhibition that, as 

 Brazilian Para rubber contained about 15 per cent, of moisture 

 as against the i per cent, of moisture usually present in culti- 

 vated Para rubber, the latex of the latter might be treated with 

 creosote and the rubber blocked, leaving a large percentage of 

 moisture, thereby saving the time and labour spent in drying 

 rubber. Rubber so prepared has not met with much favour, 

 some buyers refusing to purchase the wet block although quite 

 agreeable to accept that in a dried state. 



