Latex and its Functions. 
197 
hardly be doubled without interfering with the coagulation, 
whereas with acetic it can be increased some four times, before 
the residual liquid shows turbidity. 
The following reasons are suggested for this behaviour of 
Hevea latex towards acids. The latex is slightly alkaline. 
The proteid is of such a nature as to be insoluble in neutral 
solution, but soluble in alkaline or acid media, i.e. it is an 
alkali-albumen. When the alkalinity is neutralized by the 
necessary amount of acid, the proteid comes out of solution 
and produces with the globules of caoutchouc the clots of 
rubber. If excess of acid be added, then the proteid remains 
in solution, being now in an acid medium. The acid required 
for coagulation bears a definite ratio to the quantity of pure 
latex only, no matter what its dilution may be, because the 
alkalinity is not altered in amount by this dilution. Acetic, 
being a weaker acid than the others, does not bring about 
the changes so rapidly. 
The effect on this latex of several saline solutions has also 
been tested, viz.—sodium chloride, alum, ammonium sulphate, 
magnesium sulphate and mercuric chloride (corrosive sub¬ 
limate). The last-mentioned has the strongest and most 
complete coagulating power on the latex. With 0-3 grams 
and upwards per 100 c.c. of pure latex, all the caoutchouc 
is separated by it from the diluted latex. This is what 
might be expected, since this salt is one of the strongest 
precipitants for proteids. Magnesium sulphate is the next 
best coagulator. A one per cent, solution brings about a fairly 
complete coagulation. Ammonium sulphate has to be added 
until as much as 5 per cent, is present, before coagulation is 
anything like complete. Sodium chloride never brought 
about a complete coagulation; whatever its strength the 
residual liquid was always quite milky. Alum was more 
effective. With an amount between 1-5 per cent, and 3 per 
cent., nearly complete coagulation was brought about, but 
above and below this the process was incomplete. 
The amount of proteid present in this Hevea latex is con¬ 
siderable. By analyses kindly made for me by Mr. Kelway 
