obtained approximately pure by the solution of crude rubber iii 
benzine, allowing the insoluble matter to settle out, and subse- 
quently precipitating the rubber from the clear solution by the 
addition of alcohol. 
When pure it is practically colourless and is considerably lighter 
than water. 
It is quite insoluble in water and alcohol, which however are 
absorbed to some extent by the rubber which swells up in conse- 
quence, In turpentine, petroleum spirit, carbon bisulphide, ben- 
zole, and chloroform, rubber can be dissolved; the ease with which 
the solution vs effected depending largely upon the physical con- 
dition and history of the sample. Strictly speaking these solutions 
of rubber are solutions of the solvents in the rubber rather than 
solutions of the rubber in the liquids. This property of forming 
solutions with certain liqu ds may be of practical use as a rough 
test for the purity of rubber when ready for the market, and may 
be used to detect any* mechanical impurities such as dirt and frag- 
ments of bark. It is however, seldoip, if ever, that Para rubber 
can be prepared which will give a clear solution in these solvents, 
and this is owing to an impurity which is associate 1 with the rub- 
ber from the first and which is quite insoluble in the rubber solvent 
although swelling up and becoming quite conspicuous. This sub- 
stance, which formerly was regarded as an insoluble form of India 
rubber itself, has been shewn by WEBER to be quite distinct in 
character but never to be present in more than a comparatively 
insignificant amount. If the rubber be masticated, that is, mecha- 
nically kneaded and worked, before attempting to bring it into 
solution, this impurity ceases to appear in the solution owing to 
the state of minute division into which it has been brought by the 
mechanical treatment, but though not apparent, it is actually pre- 
sent just as before. If a dilute solution, of crude lubber in benzole, 
one part of rubber to forty of benzole, be allowed to stand for 
several weeks all this gelatinous bulky insoluble residue subsides 
into a thin film at the bottom of the vessel and the quantity is then 
clearly seen to be quite insignificant. To effect this solution of 
crude’ dried rubber in benzole or oth-r solvent, is a simple experi- 
ment which should be made by all interested in the preparation 
of rubber — the rubber strips should be put in a bottle with about 
forty times its weight of benzole, tightly stoppered and shaken at 
intervals. The rubber will be apparently in complete solution in 
two days and the nature of the insoluble residue can be conve- 
niently' studied. The action of heat upon crude India rubber is 
well marked; the heating results in a decrease of the elasticity 
with marked increase of the stickiness of the rubber, as long as the 
heat is quite moderate and not much above ioo°C.: this result is 
largely to be attributed to the presence of resin and gums which 
exist as impurity in the rubber. The resins are, in the case of 
Para rubber, of lo\v melting point, and though the percen age is 
small, not usually more than 3‘5 %, yet the effect of this small 
amount is most marked. This has an important bearing on the 
