116 PARA RUBBER. 



time. Coagulation may take place immediately or after several 

 hours' standing, according to the condition of the latex. Great care 

 must be taken to use a sodium sulphate of entirely neutral reaction. 



" What actually happens is this : The diluted rubber milk, freed 

 from all its mechanical impurities by straining, is, to begin with, ren- 

 dered non-coagulable by the addition of the formaldehyde. On add- 

 ing to the rubber milk the solution of sodium sulphate the rubber 

 substance rapidly rises to the top, where at first it forms a very thick, 

 creamy mass, the individual globules of which rapidly coalesce. The 

 coalesced (and as a matter of fact, not coagulated) mass, on being 

 worked upon the washing rollers, undergoes a very curious polymeri- 

 sation process, and thereby rapidly acquires the great strength and 

 toughness so characteristic of high-class indiarubber. 



" On cutting the cake open it will be found to be rather spongy, 

 being full of little holes which are still filled with some of the albu- 

 minous, though very dilute, mother liquor. If, therefore, the rubber 

 were dried in this state, it is obvious that it would still contain a small 

 quantity of the objectionable albuminous matter. For this reason 

 the rubber so obtained should at once be taken, cut into strips, and 

 subjected to a thorough washing upon an ordinary rubber washing 

 machine." The formalin acts more as an antiseptic to prevent 

 the decomposition of the proteid than anything else, and does 

 not affect the specific gravity of the rsother liquor. 



Johnson made several attempts, when in the Gold Coast last year, 

 to separate rubber from Para latex in the manner above suggested, 

 but failed in each instance, although the latex stood, in one or two 

 instances, for nearly three weeks without the rubber separating out. 



This method has been tried by many persons, and evidently 

 requires further experiments before it can be pronounced as perfect. 

 It should be remembered that certain reagents e.g. ammonia, 

 serenguiana, &c, will keep the latex in a liquid state for a very long 

 time, and might be used with advantage in such experiments. 



Rapid Coagulation and Removal of Proteids by 

 Mechanical Means. 

 It has been stated that mechanical appliances have been invented 

 which can effectively eliminate the proteid while forming part of the 

 latex 



Biffen's Centrifugal Machine. 

 Biffen* recognized that in latex the indiarubber existed as 

 suspended globules, lighter than water, and employed for 

 separating the caoutchouc, a centrifugal machine similar to that used 

 in separating butter from milk. The machine is a modified form of 

 the ordinary centrifugal milk tester, capable of being rotated 6,000 

 times per minute. The caoutchouc of Para latex is said to be 

 effectively separated in a few minutes and to consist of the pure 



♦Biffen; Annals of Botany, June, 1898. Journal of the Society of 

 Arts, 1898. 



