326 Prof. Johnston on a new Compound of 



'^^! yj^fi\g^^^^^y «f '^^ "^^ ^^^'1 = 2-753 and 2-76 1 

 at 60 i^ahr J 



After heating to redness = 2*936 and 2*929 



Its density, therefore, as we should expect, lies between 



those of gypsum and anhydrite, and after heating to redness 



it has precisely the specific gravity of the latter. 



Density of gypsum = 2*310 Mohs, 2*322 Royerand Dumas. 



new salt = 2*757. 



anhydrite = 2*899 Mohs, 2*96 Royer and Dumas. 



r new salt-1 ^ 2*932. 



alter heatmg j 

 The boiler in which this deposit is formed is worked under 

 a pressure of nearly two atmospheres, and to this among other 

 circumstances is probably due the formation of this sin- 

 gular hydrate. When sulphuric acid is added to a dilute 

 boiling solution of chloride of calcium, crystals of gypsum 

 with the usual quantity of water are deposited. Added hot 

 to a solution of chloride of calcium which boiled at 265° Fahr., 

 an earthy precipitate fell, which after drying at 212° lost by 

 a red heat only 1*43 per cent. The temperature of a more 

 dilute solution boiling at a heat of 220° to 230° Fahr. falls in- 

 stantly to 212° Fahr., on the addition of a drop of hot sul- 

 phuric acid ; the sulphate formed causing a copious evolution 

 of vapour. I have therefore not succeeded in my attempts 

 to form this salt artificially. The uniform high temperature 

 maintained under a higher pressure than that of the atmo- 

 sphere may be the chief cause of the formation of the salt in 

 the steam boiler. 



Is this salt a simple hydrate 2 Ca S + H, or is it a com- 

 pound salt Ca S + Ca SH, or 3 Ca S + (Ca S + 2 H) ? This 

 question is entirely theoretical, the properties of the salt 

 lending no direct support to either opinion. It is, however, 

 not without interest in the present state of our knowledge in 

 regard to the water contained in salts. The observation made 

 in regard to the superior affinity of many sulphates for one in 

 preference to the other atoms of water which their crystallized 

 hydrates generally contain, does not apply to the sulphate of 

 lime, and the existence of this half hydrated crystalhzed com- 

 pound — if considered as a simple salt2CaS + H — is equally 

 inconsistent with the idea expressed by the term saline water. 

 If by this term it is intended to denote that of the 6 or 7 

 atoms of water with which certain sulphates combine, one of 

 these equivalents performs a peculiar function, we have in 

 the present salt half an atom only remaining, and this driven 



