264 PETER SPENCE 



The formation of cement, which he calls 

 Patent Zinc Cement, from the spent shale 

 after the sulphate of ammonia was washed 

 out was another item of this most inclusive 

 patent. 



He took two parts of refuse lime from 

 the gas works, and one part of his spent 

 shale, and to that he added a little sulphate 

 of zinc solution ; these are mixed to about the 

 consistence of mortar, made into bricks, 

 dried, and afterwards calcined or burned at a 

 moderate red heat ; after cooling it is finely 

 ground and constitutes cement. 



The zinc was used for two purposes; to 

 prevent the oxydisation of any iron, causing 

 the colour of the stone to be degraded, and 

 also to prevent the stone being attacked by 

 mosses and lichens. 



The last point he claimed is one of much 

 interest ; it related to the manufacture of the 

 carbonates of the alkalies from the sulphates 

 by means of sulphate of baryta. 



Powdered sulphate of baryta was mixed 

 with carbonaceous matter and heated. After 

 this mixture is burnt it is lixiviated, and a 

 solution of sulphide of barium is obtained ; to 

 this the sulphate of the alkalies (in solution) 

 is added, sulphate of baryta is thrown down, 



