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XLIII. On a new Compound of Sulphate of Lime *with 

 Water. By James F. W. Johnston, F.R.S., Sfc. ^c* 



T N the boiler of a steam-engine worked at Team Colliery 

 -*- near Newcastle, and fed by water from the mine, a bright 

 steel-gray granular deposit has been several times observed, 

 which under the microscope appears to consist of small trans- 

 parent prismatic crystals discoloured by carbonaceous matter. 

 The faces of these crystals are rounded, but according to 

 Mr. Brooke, they are right rhombic prisms, the angles being 

 undeterminable with any degree of accuracy. 



Heated in a close vessel these crystals give off pure water, 

 becoming opake, and at a red heat in the air they lose their 

 colour and become white. Heated to 220° Fahr. in the air 

 they lose a sensible quantity of water, and kept at 240° Fahr., 

 for a couple of hours the whole of the water is driven offj so 

 that at a higher temperature they undergo no further loss, 

 except what is due to the combustion of the small quantity 

 of carbonaceous matter they contain. 



Boiled in distilled water they are very sparingly soluble : the 

 solution gives white precipitates with chloride of barium and 

 oxalate of ammonia. 



After drying at 212°, ] 9-424' grs. lost 1"25 = 6-435 per 

 cent, when heated in a close vessel till all the water was driven 

 off. The colour was still gray. Heated to redness in the air 

 till it became white, the loss amounted to 6*728 per cent., 

 giving 0*293 per cent, for carbonaceous matter. A second 

 portion of 25*194 lost 1*742 when heated to redness in the 

 air = 6*914 per cent. 



Of the white salt thus heated in the air, fused with car- 

 bonate of soda, digested in distilled water, filtered, and pre- 

 cipitated by chloride of barium, gave 



Anhydrite by calculation 

 contains 



Lime 41'734 41*532 



Sulphuric acid ... 59*027 58*468 



The salt therefore consists of 



Sulphate of lime = 93*272 



Water = 6*435 



Carbonaceous matter = 0*293 100* 



The formula Ca S + 4 H gives 



Sulphate of lime = 93*843 



Water = 6*157 100* 



• Communicated by the Author. 



