14 ON THE COMMERCIAL KINDS OF INDIA-RUBBER. 
gallon of the milk. This is done in a large tin pan, in which it 
coagulates quickly, forming a soft mass floating in a brown fluid, and 
smelling like fresh cheese. This mass is slightly pressed by hand, 
placed on a board, and then rolled out with a piece of heavy wood. 
I have used with advantage an iron roller 150 lbs. in weight for this 
purpose. By this operation a great quantity of dark brown water is 
squeezed out, and the rubber, which has now assumed its elasticity, is 
in flat round pieces of + to $ inch thick by 20 inches in diameter, anc 
perfectly white. The weight of one of these pieces (*tortillas* the 
men call them) is about 7 lbs. The tortillas are hung up ina shed on 
poles to dry, which in fair weather takes about a fortnight ; the rubber 
assumes then its dark colour, and weighs 2 lbs. a piece. If the vine 
is not to be had in the neighbourhood, two third parts of water are 
mixed with one-third of the extracted milk in a barrel, and this has to 
remain undisturbed for twelve hours ; after this time the water is slowly 
discharged, and the residue—a dark cream—is put in vats made in the 
ground, and left to dry. The drying process takes from twelve to 
fourteen days.'' 
Mr. N. Burgess, of Hackney, enables me to give the fion. 
ing notes on the microscopie structure of caoutchouc :—“' In t 
dry sections of the different kinds no trace of any structure, save lis 
mechanical laminated appearance, is observable. The identity in cha- 
racter between Guatemala, Guayaquil, Carthagena, and the so-called 
West India rubber, is very apparent. The resinous contents of Gua- 
temala rubber look like so much Kowrie gum. Under polarized light, 
the substance has a somewhat granular appearance, possibly owing to 
the different degrees of purity of the substance itself acting by refrac- 
tion ; dissolved in chloroform, no trace of any structure, granular or 
nus i is perceivable.” 
Micrandra siphonioides, Benth., and M. minor, Benth., afford caou- 
_ tchouc equal in their elasticity to that of the Heveas ; but of their colour 
or other properties I cannot at present obtain any information. 
Dr. Spruce collected a small piece of excellent caoutchouc, about the 
size of a walnut, from Siphocampylos Jamesonianus, DC.; but, as the 
plant is a mere herb, it cannot prove of any great abeinebeeetal i impor- 
tance. 
IL. ASIATIC KINDS OF INDIA-RUBBER. 
The attention given by different travellers and others to the rubber 
