TRANSACTIONS OF SECTION B. 525 



but the relative quantities of these products varied in the two cases. The ex- 

 planation may be that the ozonides of indiarubber and guttapercha are not 

 identical but stereoisomeric. Stereoisomerism in the fundamental C,ori,c hydro- 

 carbon is not possible if the formula proposed is correct, although there is this 

 possibility in the case of the ozonides. Attempts are being made to isolate the 

 dimethyloctadiene, but these have up to the present proved unsuccessful, the solution 

 of the problem being attended with great difficulties. 



3. 071 the Polymerisation of Isoprene. 5y Professor W. A. Tilden, F.R.S. 



Many years ago I showed that the principal terpenes, when decomposed by heat, 

 yield, among other products, a small quantity of isoprene, C^H^. The constitution 

 of this compound has since been shown by Euler ^ to be expressed by the formula 

 CHj : OH . CMe : CH^. When kept for a long time isoprene is slowly converted 

 into indiarubber, the process, however, occupying many years. The specimens 

 now exhibited illustrate the process of transformation. If any attempt is made 

 to hasten the operation, as by heat or contact with strong reagents, the greater 

 part of the hydrocarbon is converted into dipentene and the mixture of viscid 

 compounds of high boiling-point, known as colophene, which results from the 

 polymerisation of the terpenes. Dipentene has the formula — 



AfCH — CHov ^CHj 



CHj . of >CH . Cf 



\CHj— CH/ \CH3 



and colophene, no doubt, also contains a number of six-membered rings. 



It appears probable, therefore, that the slow polymerisation which ultimately 

 results in the production of solid indiarubber is due to a different mode of linkage 

 leading to the formation of long chains. Except on the assumption of a shifting 

 of hydrogen this can only take place on condition of the formation of a series of 

 tetramethylenc rings, somewhat in the following manner : — 



CHj . CH . CMe : CHj CH^ . CMe . CH : CH^ 

 II or I 



CH^ . CH . CMe : CH„ CH. . CH . CMe . CH, 



II ' II" 



&c. &c. &c. &c. 



Indiarubber, though of high molecular weight, is an unsaturated substance, as 

 shown by the fact that it absorbs oxygon from the air, and unites chemically with 

 sulphur and other elements. 



4. Tlie Latex of Dyera costulata. 

 By Professor W. A. Tilden, F.R.S. 



Early in May last I received from a correspondent in Singapore a sample of 

 the latex of Di/era costulata to which a small quantity of ammonia had been 

 added, to keep it from coagulating. It remains a white creamy fluid of specific 

 gravity I'll, miscible with water. I am without information as to the reaction of 

 the original fluid with test-papers. It is rare to find vegetable juices exhibiting 

 an alkaline reaction, but I am disposed to believe that this latex in the fresh state 

 possesses slight alkalinity, as it is coagulated sooner or later by all acids, without 

 agitation. But, as in milk, the suspended particles unite when the liquid is violently 

 shaken. It is also coagulated by admixture with a strong solution of common salt, 

 and when warmed with an equal volume of 20 per cent, solution of caustic soda. 

 Heated to a temperature of 70° — 80° C, solidification does not occur except at the 

 surface, where a skin forms ; and even on boiling no immediate change takes place. 

 The milk as received yielded about 44 per cent, of solid by coagulation with 



» Per. 1897, 30, 1789. 



