78 CLAYS AND CLAY INDUSTRY. 



hoc. Lab. No. Per cent. 



77 IS 0.18 



67 20 0.06 



132 622 0.15 



101 644 0.06 



81 25 0.08 



24 13 0.18 



14 12 0.28 



67 21 0.34 



222 603 1.35 



Soluble salts in Pleistocene clays, 

 hoc. Lab. No. Per cent. 



276 726 0.30 



290 727 0.21 



291 618 0.47 



Prom these it will be seen that the samples of Clay Marl I 

 showed the highest percentage of soluble salts, and that as a 

 series, the Raritan clays showed the lowest percentage of soluble 

 salts. 



The Raritan samples tested, with the exception of locality 222, 

 are of the higher grade clays, and do not include any of those 

 used for fireproofing. It is probable that these, if tested, would 

 yield percentages as high as Clay Marl I, since they contain con- 

 siderable pyrite. 



Prevention of soluble salts. — If a brick is vitrified the soluble 

 compounds are rendered insoluble, but in the manufacture of 

 many grades of ware the clay is not carried to vitrification, and 

 therefore the soluble salts must be rendered insoluble if possible. 

 This is most effectively done by adding some chemical to the wet 

 clay which will react with the soluble salts in it, and. either render 

 them insoluble or else change them into- some very easily soluble 

 compound that can be readily washed from the surface of the 

 ware. 



The substance commonly added is either barium chloride or 

 barium carbonate. When barium salts come in contact with 

 soluble sulphates, barium sulphate is formed, a combination which 

 is absolutely insoluble in water. This is expressed by the first 

 of the following chemical reactions if barium carbonate is used, 

 and by the second if barium chloride is employed. 



