RUBBER PLANTING 157 



thus obtained is transported to the central factory for 

 further treatment. 



Coagulation. 



The principal medium employed for effecting coagu- 

 lation is acetic acid. Other coagulants are sometimes 

 employed. The merits of hydrofluoric acid have been 

 widely advertised, but the powerfully corrosive effect of 

 this substance is a disadvantage. We do not know 

 of any exhaustive comparison between the effects of 

 hydrofluoric acid and those of acetic acid. Mixtures 

 containing tartar emetic, formaldehyde and other sub- 

 stances have also been recommended. 



Fresh latex is slightly alkaline. The chemical and 

 physical nature of the process of coagulation is not 

 altogether understood, but it is generally supposed that 

 the phenomenon consists primarily in the precipitation 

 of the proteids of the latex which are soluble in an 

 alkaline medium. The coagulated proteids form a net- 

 work in the meshes of which the globules of rubber are 

 entangled, and the whole then contracts into a clot. An 

 excess of acid leads to renewed solution of the proteids, 

 so that either too much or too little acid produces 

 incomplete coagulation. The special merit of acetic 

 acid lies in the wide range of proportions in which it 

 can be added to the latex, whilst still ensuring complete 

 coagulation. Thus Parkin states that the acid can be 

 added either in quantities four times below the proper 

 amount or nine times above it, with very little waste of 



