Chemical Science. 629 



In preparing the purple precipitate of Cassius, Fischer, who first 

 pointed out the superiority of the protonitrate of tin in the above 

 experiment to the other salts of that metal, also uses the same 

 solution. It very much surpasses the protomuriate, and is always 

 successful, whether used in a weak or a concentrated state. 



When protonitrate of mercury is poured into solution of gold, 

 according to Fischer, a blue grey precipitate is obtained, quite in 

 analogy with the purple of Cassius. It is composed of deutoxide of 

 mercury and suboxide of gold, and is not decomposed by muriatic 

 acid ; that substance only dissolves a little mercury, and makes the 

 colour of the remaining precipitate pass to a clear grey white*. 



19. (ENOMETER OR ALCOHOMETER. (By M. Emile Tabarie.) 



This instrument is* intended to supply the manufacturer with the 

 means of ascertaining the quantity of spirit in any vinous liquid. 

 The principle consists in boiling the wine (for instance) in the open 

 air, allowing the alcohol to escape, and making up the bulk of the 

 residue by the addition of pure water. The difference between the 

 density of this mixture and the original liquid indicates the quantity 

 of alcohol which was present. The apparatus consists of a small 

 boiler heated by a spirit lamp ; a horizontal cross bar near the bot- 

 tom, when left uncovered by the liquid, indicates when the ebullition 

 has proceeded so far as to ensure dissipation of all the alcohol. The 

 densities before and after ebullition are ascertained by a hydrometer 

 with a double scale. For correction of temperature, a thermometer 

 with double scale is used, one scale being the Centigrade, and the 

 other a peculiar division, intended to simplify the operation. Tables 

 accompany the instrument. The whole is intended for the distillers 

 of the centre of France, and costs about forty francs t- 



20. ON THE MANUFACTURE OF SULPHURIC ETHER. (C. Wittstock^) 



The remark of MM. Fourcroy and Vauquelin, that the sulphuric acid 

 employed in the fabrication of ether undergoes very little change, led 

 to the conclusion that ether would be formed as long as there was a 

 fresh supply of alcohol to the acid. This supposition was confirmed 

 by the experiments of M. Gay-Lussac ; and since then the fabrication 

 of ether has been considerably improved by MM. Boullay, Geizer, 

 and others. I have for some time employed the following method ; 

 and as I am disposed to consider it more simple and less expensive 

 than any other, a short description of it may perhaps be acceptable 

 to the reader. 



A mixture of nine parts of sulphuric acid (s. g. 1.84 1 .85), and five 

 parts of alcohol (s. g. 0.835) are put into a green glass retort of one 

 foot in diameter, with a glass tube inserted at its upper part. This tube 



Jour, de Pharm. 1831, p. 175. f Aim, de Chimie, xlv. 222. 



VOL. I. MAY, 1831. 2 T 



