598 SCIENCE PROGRESS 



Henri makes no mention of the albuminous matter present 

 in the latex, and so it is to be inferred that he regards the 

 coagulating reagents as acting directly on the caoutchouc 

 globules, causing them to agglutinate. But his facts are readily 

 explained otherwise. The dialysis will only remove the salts and 

 not the proteins. Now the clotting or separating out of colloids, 

 such as proteins, is influenced by the presence of salts. When 

 these latter are removed the proteins in solution will behave 

 quite differently towards the various reagents employed for 

 separation ; hence the coagulation of the latex, when dialysed, 

 will not be able to be effected in the same manner as that of 

 the fresh latex; at the same time the clotting will be due none 

 the less to the protein present. On such reasoning the coagula- 

 tion of latex will be brought into line with the facts now known 

 respecting the so-called " strength " in wheat flour and the 

 behaviour of proteins generally in regard to precipitation. 



Two matters of great importance from a practical point of 

 view deserve to be noticed in regard to coagulation. In the 

 first place the reagent employed has in all probability a specific 

 influence on the quality of the rubber produced and especially 

 on its behaviour in vulcanisation. 



Secondly, coagulation alone is not sufficient. It should be 

 combined with curing. Rubber prepared by acetic acid will 

 mould and deteriorate if not kept dry. Hence in the Ceylon 

 experiments creosote was used .and recommended as a pre- 

 servative. This, however, does not seem to be generally 

 practised. Much of the plantation rubber now on the market 

 is not cured, but being produced in thin sheets it dries rapidly 

 and so reaches London, as a rule, in good condition. 



There is no doubt, however, that cured plantation rubber 

 will in the future gain the favour of the market. It is significant 

 now that what is known as " smoked sheet " commands the 

 highest price. It remains to be seen whether a convenient 

 wet method of coagulation can be introduced which will 

 produce a satisfactorily cured rubber. If the coagulant and 

 preservative can be combined in one reagent, so much the 

 better. Formic acid, mercuric chloride and " Purub " have 

 this double property, if any of them may prove satisfactory 

 otherwise. If acetic acid be adhered to, then some antiseptic 

 must be supplied in addition. 



This apparent necessity of curing the rubber has focussed 



