196 
Parkin.—Observations on 
about the coagulation quite as completely, but not so quickly, 
in the cold. The approximate weight of acid required to 
completely coagulate 100 cubic centimetres of pure latex has 
been worked out for the following acids :— 
Sulphuric acid 
o*i gram 
clots 100 c.c. latex. 
Hydrochloric acid 
o-i „ 
55 5 5 
Nitric acid 
o *3 „ 
55 55 
Acetic acid 
o -95 „ 
5 > 55 
Oxalic acid 
0-2 „ 
55 »> 
Tartaric acid 
0-25 „ 
55 55 
Citric acid 
o *5 „ 
55 55 
The first two are thus seen to be the strongest coagulators, 
while acetic acid is the weakest, nearly ten times as much 
being required. 
Two special points are to be noticed regarding this acid 
coagulation. 
In the first place, the quantity of acid needed depends 
only on the amount of pure latex present in the liquid to 
be clotted. A certain weight of acid is required to completely 
coagulate 100 cubic centimetres of latex, no matter whether 
this be diluted to five or ten times its bulk. In other words, 
doubling the dilution halves the acid for a given volume, 
e g., 100 c.c. of liquid containing 5 c.c. of pure latex requires 
half the amount of acid necessary for 100 c.c. of liquid 
containing 10 c.c. of latex. The latex can be diluted to any 
extent, and yet its particles of caoutchouc are capable of 
being collected together into clots by the addition of the 
necessary quantity of acid. This was even done for latex 
diluted 2,000 times. 
In the second place, if the acid be added to excess, above 
a certain amount, coagulation ceases to be complete. By 
complete coagulation is meant the removal from suspension 
of all the globules of caoutchouc, so as to leave the liquid 
quite clear. The range for complete or nearly complete 
coagulation is very small with all the acids employed, except 
acetic. With sulphuric acid, for example, the amount can 
