306 Progress of Foreign Science. 



cury, pass speedily from yellow to black ; we can obtain even 

 immediately black precipitates with these re-agents, if we employ 

 very concentrated solutions. The precipitate by sulphate of 

 zinc becomes slightly greenish on exposure to air. The others 

 do not change their colour either in air or water. None of them 

 effervesces either with the sulphuric or muriatic acid. 



A solution of hydroxanthate of potash, very neutral, enclosed 

 in a vessel which screens it from the action of the air, may be 

 heated during half an hour at a temperature of 60° C. without 

 losing its characteristic properties. But, if before heating it, we 

 have rendered it alkaline by an addition of potash, it will soon 

 acquire the property of precipitating the salts of lead black. 



If we gradually heat the hydroxanthate of potash enclosed in 

 a small retort, communicating with a receiver, from which a tube 

 passes into a mercurial bath, the following circumstances take 

 place : Before the temperature is raised beyond 60° C. the salt 

 appears to undergo no change; when heated more strongly, it 

 yields oleaginous vapours, fuses with a strong effervescence, 

 producing abundance of gas ami vapours, and is transformed 

 into a mass of a blood-red colour. The vapours soon condense 

 into a liquid, which has the appearance of oil. The red matter 

 hardly clianges its colour on cooling. On exposing this sub- 

 stance to a higher temperature than that at which it was pro- 

 duced, it enters anew into an effervescing fusion, blackening at 

 the same time, and giving rise to much oil and a little gas. But, 

 at the end of some time, the frothing ceases ; and finally the 

 mass, quietly melted, produces neither oil nor gas, even at a 

 temperature not far from that of a cherry-red. On allowing the 

 mass then to cool, it divides itself into two portions, of which 

 the lower is manifestly crystalline, of a black grey, and a lustre 

 almost metallic ; whilst the upper layer, of a nearly black colour, 

 has no crystalline texture. If the fire be pushed so as to keep 

 the mass red for some time, it will not furnish the crystallized 

 part. The gaseous product appears to be of the same kind 

 during the whole course of the decomposition ; the same holds 

 true of the oily matter. The first is distinguished by an ex- 

 tremely strong odour of onions or leeks ; but, in other respects, 

 it comports itself (at least in trials with contact of water) like a 

 mixture of carbonic acid gas and sulphuretted hydrogen. 



Xanthic Oil. — This liquid is limpid, and of a yellowish colour. 

 Its odour (which resembles neither that of carburet of sulphur 

 nor sulphuretted hydrogen) is very strong, and adheres strongly 

 and for a long time, to every body which has been impregnated 

 with it. Its taste is at once saccharine and pungent. Water 

 appears to dissolve it in very small quantity; alcohol, when 

 diluted even to a great degree, dissolves it in abundance. The 

 alcoholic solution is disturbed by a certain quantity of water; 

 but, if not too much loaded with oil, it becomes clear, on the 



