THE AFRICAN RUBBER TREE 175 



heating is continued until the sohition is left clear. The 

 rubber thus obtained is at once rolled out into a sheet by 

 means of a wooden roller, and is subsequently well washed 

 and dried. 



Fresh latex, it may be observed, is very difficult to 

 coagulate completely by boiling ; but if the latex is allowed 

 to stand for tAN'clvc hours before being treated, the process 

 is quite easy and effective. 



It is stated that the latex may also be conveniently 

 coagulated by passing steam into it. 



Addition of Coagidants. — The principal coagulants which 

 have been proposed for preparing Funtumia rubber 

 are tannic acid, mercmric chloride (corrosive sublimate), 

 and formalin. 



If Funtumia latex which has been kept for a few days 

 be diluted with hot water and a solution of tamiic acid 

 or merciu-ic chloride added, complete coagulation is im- 

 mediately induced ; but if fresh latex be used, only slow 

 creaming takes place. Christy states, however, that if 

 a little acetic acid be added to the fresh latex diluted 

 with hot water, the addition of tannic acid or mercuric 

 chloride then produces unmediate and complete coagula- 

 tion, although the acetic acid has no coagulating action 

 hy itself. Hot water is essential for the success of this 

 method, as if cold water be used only slow creaming takes 

 place with both fresh and old latex. 



The process recommended by Christy for the coagula- 

 tion of fresh Funtumia latex by means of tannic acid is 

 as follows : 



A stock solution of tannic acid is made by dissolving 

 1 lb. of tannic acid in 16 oz. of water and adding 5 oz. 

 of acetic acid. 1 oz. of this solution is poured into 20 

 pints of hot water at 80° F., and 5 pints of fresh latex 

 are then added and well mixed with the acid solution. 

 Coagulation quickly occurs and may be facilitated by 

 gentle agitation of the vessel. 



Mercm-ic chloride may be employed in the same way, but 

 on account of its very poisonous properties it is not so 

 suitable as tannic acid for general use. 



Funtumia latex can also be coagulated by the addition 

 of formalin (formaldehyde), which is frequently added 

 to other latices to retard their coagulation. According 

 to Christy, the addition of 15 cc. of commercial formalin 



