Nature of the Vesicating Constituent of Croton Oil. 247 



which agree best with the formula Ci 3 H 18 4 , the calculated percentages 

 being 



C = 65*54 per cent. ; H = 7'56 per cent. 



Croton-resin is nearly insoluble in water, light petroleum, and 

 benzene, but dissolves readily in alcohol, ether, chloroform, acetic 

 ether, and amyl alcohol ; and is deposited, even by the very sJow 

 evaporation of these solvents, as a pale yellow resin. Its solution 

 produces no effect on polarised light. The resin has no fixed melting 

 point. A few degrees above the atmospheric temperature it softens 

 and very gradually melts as the temperature is raised being quite 

 fluid at 90° C. 



Croton-resin has neither basic, nor acidic properties. It is insoluble 

 in dilute acids ; and nearly so in solution of sodium carbonate from 

 which it can be extracted unchanged by shaking with ether. It 

 does not act with metallic oxides and may be boiled w r ith a mixture 

 of water and lead oxide without being appreciably affected. On 

 the other hand it is very slowly decomposed and dissolved by contact 

 with aqueous caustic alkalis and is very rapidly changed if heated 

 with them, the resin being gradually dissolved with much darkening 

 in colour and eutire loss of its vesicating power. Ammonia acts 

 much less rapidly. Water, heated with the resin in a closed tube at 

 200° C, slowly decomposes it, with formation of a dark coloured 

 resin and a mixture of acids. Dilute acids, also, slowly decompose 

 the resin when heated with it in a closed tube at 200 — 250° C. ; 

 much darkening in colour takes place and several acids are formed, 

 but they have not hitherto been obtained in sufficient quantity to 

 separate and identify. One would appear to be valerianic acid. As 

 the total quantity of pure material at oar disposal has been very 

 small, it has not been possible, so far, to do much towards elucidating 

 the question as to the constitution of croton-resin. This seems to 

 be complicated, since on decomposition with alkalis it furnishes a 

 mixture of acids, some of which seem to be higher members of the 

 acetic series. When the resin is heated with strong potash solution 

 (50 per cent.), it is quickly decomposed, a bla,ek resinous mass being 

 produced in addition to " soap," from which a mixture of fatty acids 

 was liberated. A very small quantity of one of these was separated 

 in a nearly pure state as an oil at the ordinary temperature. It 

 appeared to be oleic acid, since its silver salt contained 26'38 per 

 cent, of silver, whilst silver oleate contains 27 per cent. When the 

 resin is heated with a 10 per cent, solution of soda in a closed tube 

 at 100° C. it completely dissolves. As is usually the case, when the 

 resin undergoes hydrolysis, a dark coloured quite inactive resin, 

 insoluble in ether, is produced, together with a mixture of acids. 

 When the solution is acidified and distilled, a small quantity of a 



