to3 



haps by the same means. Some can be coagulated by heat, others 

 cannot. Most can be coagulated by either acetic or dilute mineral 

 acid but all can be immediately coagulated by a solution of tannic 

 acid, hydro-ferrocyanic acid or mercuric chloride or nitrate. .Rub- 

 ber thus coagulated contains all the albumen; the amount of which 

 varies in different rubbers, thus Para rubber contains not more 

 than 2-3 per cent, while coagulated Castilloa contains often as 

 much as 4 per cent. 



It is this albuminous matter in the rubber which produces 

 "heating", due to the putrescence of the albuminoids. Rubber 

 free from albumen never "heats" and this putrescence cannot 

 occur if the rubber is perfectly dry. The incorporation of some 

 antiseptic substance also prevents it. This latter is what is affected 

 by the smoking of Para in the usual method, in which the acetic 

 acid in the smoke probably acts as the coagulating agent the 

 creosote and similar bodies act as antiseptics. 



The comparative impurity of crude rubber stated as loss in wash- 

 ing or shrinkage by the manufacturer. These impurities which 

 have lately decreased in African rubbers, but have been growing 

 worse and worse in American and Eastern rubbers are mechanical 

 impurities, earth, bark, &c. and resin and albuminoids. 



The former are easily removed by straining. To remove the 

 albuminoids Dr. WEBER recommends the following: — Add to 

 every gallon of latex \ oz. to 1 oz. of formaline (40 pc. solution) 

 stir the latex and allow to stand one hour. Then add a solution of 



1 lb. sodium sulphate in one pint of boiling water while hot and 

 stir. Coagulation mav take place immediately or after several 

 hours standing. The sodium sulphate must be entirely neutral 

 (not acid). 



The cake is liable to contain numerous cavities including some 

 of the molten liquor. It should therefore be washed on a corru- 

 gated rubber washing machine, then thoroughly dried in a dark, 

 well ventilated shed. This rubber will be found to be free from 

 every trace of albuminous matter and its only impurity will be the 



2 pc. of resinous matter. Strictly speaking this rubber is not 

 coagulated as the albuminous matter is removed but coalesced. 

 The formaline combines with the albumen and forms a readily 

 soluble solution. The sodium sulphate causes the rubber to rise 

 to the top in a creamy mass and coalesce, and on working it on 

 the washing rollers it rapidlv acquires the great strength and 

 toughness of high class rubber. Of coagulants Dr. Weber men- 

 tions a number several of which would however, spoil the rubber. 

 But he mentions four, vis., formic acid, acetic and tannic 

 acids, and phenol as more suitable. Of these tannic acid is the 

 most energetic, but the rubber so prepared if wet and put into an 

 incubator of ioo° Fahr. putrities. Formic acid and acetic are 

 less energetic. The former is more expensive but less is required 

 in the proportion of 3 to 4. It also has the advantage of posse^sini; 

 distinct antiseptic properties. 



No more of the acids should be used than is absolutely required. 



