treatment of freshly coagulated and pressed ‘'biscuits’' of rubber. 
Anything in the way of heating to accelerate the drying of the 
biscuits is to be avoided and increased rapidity must be ob- 
tained by the employment of currents of drv air passing over the 
biscuits which must also be kept as thin as possible if rapid drying 
is desired. On heating India rubber to a greater extent, it melts 
and then begin to decompose, breaking down into various liquid 
products which can be distilled off. 
On heating with free exposure to air the rubber takes fire and 
burns freely. It is not commonly realised how inflammable India 
rubber is, and to obtain real conviction of this property a small 
strip of dry rubber should be burn!. 
With the majority of chemical re-agents India rubber shews no 
action, this being a property which it holds in common with many 
other hydro-carbons. It does, however, re-act with the strong 
mineral acids, and with chlorine and bromine. Its re-action with 
sulphur is the most important, if heated wifh this substance (or 
if a solution of rubber be treated with sulphur monochloride) the 
rubber combines with the sulphur and becomes both chemically 
and physically more inert than before. This process of combina- 
tion with sulphur is called vulcanisation and after vulcanisation 
the rubber is no longer soluble in the solvents mentioned, nor, 
which is more important, does it become sticky on gentle heating, 
nor brittle when exposed to cold. In fact if it were not for this 
capacity India rubber possesses lor absorption of, and combination 
with sulphur and consequent change of properties, the India rubber 
industry could scarcely have developed at all. 
The amount of sulphur which can be combined with the rubber 
in the process of vulcanisation varies from a lower limit of about 
3 per cent, to an upper limit of 32 per cent., and the product 
becomes harder and darker as the amount of sulphur is increased 
until hard rubber, that is vulcanite and ebonite, results when 20 
per cent, of sulphur has been combined with the rubber. Between 
these limits there is every gradation of product possible. 
Towards oxygen and oxidising agents generally, rubber is com- 
paratively inert, but with the oxygen of atmospheric air there is 
some slight action resulting in the formation of a resinous oxida- 
tion product. As might be expected this action in its rapidity 
depends upon the porosity and condition of the rubber with respect 
to the amount of surface exposed: with crude rubber, as prepared 
from the latex, this action in a period of six months appears to be 
quite negligable, and little fear of deterioration of the rubber 
during its transport to Europe need be apprehended. 
The foregoing account of the properties of rubber is extremely 
brief, fuller details and a further account of many points not even 
touched upon, can be found in Weber’s Chemistry of India Rubber. 
In my next letter I propose to consider the other constituents of 
the latex and then shall deal with practical methods of preparation 
