io3 
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 drv. 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 4 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 may 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 sonic: 
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 rapidly 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, viz., 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 loo 0 Fahr. putrifies. Formic acid and aqetic 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 possessing 
distinct antiseptic properties. 
No more of the acids should be used than is absolutely required. 
