ix SULPHUR AND PHOSPHORUS 171 



describes how sulphur may be dissolved in potash made 

 caustic with lime, and states that the clear solution becomes 

 milky on the addition of vinegar, yielding a sediment of 

 finely divided sulphur. Glauber, too, records the fact that 

 flint and rock-crystal, which are insoluble in acids, may be 

 dissolved by means of alkalis and precipitated again by 

 adding an acid. 



The solutions of sulphur in alkalis were described as 

 LIVER OF SULPHUR and were used extensively in medicine 

 and in the preparation of pure MILK OF SULPHUR, made 

 by dissolving the sulphur in an alkali and then precipitating 

 it again with acid. 



Sulphuretted hydrogen. When liver of sulphur is acted 

 on by acids, only a portion of the sulphur can be recovered ; 

 a considerable part is lost in the form of a " foetid gas 

 having the odour of bad eggs " ( Hoffmann, 1772). This gas 

 possesses the property of blackening silver vessels (Boyle, 

 1663), is inflammable (Meyer, 1764), dissolves readily in 

 water, 1 and is present in natural sulphur- waters, from which, 

 on exposure to the air, sulphur is deposited. On account of 

 its method of preparation from liver of sulphur it was 

 generally described as HEPATIC GAS. Scheele (on 

 " Stinking sulphureous Air," Essays on Air and Fire, 

 pp. 186-193) showed that it could be prepared from 

 sulphur by heating it in hydrogen, and that the sulphur 

 could be recovered from it by the action of oxidising 

 agents (nitric acid and chlorine) ; he therefore regarded 

 it as produced by the union of sulphur with phlogiston. 

 This view was modified by Lavoisier and his colleagues, 

 who regarded it as a compound of sulphur and hydrogen, 

 and gave to it the name of SULPHURETTED HYDROGEN. 



Composition of sulphuretted hydrogen. When sparked, 

 sulphuretted hydrogen is decomposed, sulphur being de- 



1 "Water absorbs just its bulk of this gas ; when, therefore, it is mixed 

 with hydrogen, this last will be left after washing in water, or what is 

 still better, in lime-water " (Dalton, New System, II. 452). 



