CHEMICAL PROPERTIES OF CLAY. 79 



1. CaS0 4 + BaC0 3 = CaC0 3 + BaS0 4 . 



2. CaS0 4 + BaCl 2 = CaCl 2 + BaS0 4 . 



We thus see that in both cases we get compounds which are 

 insoluble or nearly sol If soluble sodium compounds are present 

 the addition of barium carbonate or barium chloride will form 

 either sodium carbonate or sodium chloride (common salt), but 

 since both of these are easily soluble in water they can be washed 

 off without much trouble. 



Method of use. — As carbonate of barium is insoluble in water, 

 in order to make it thoroughly and uniformly effective it should 

 be used in a finely powdered condition and distributed through 

 the clay as thoroughly as possible, because it will only act where 

 it comes into immediate contact with the soluble sulphates. 

 While only a small quantity of barium is necessary, still it is 

 desirable to use somewhat more than is actually required. 



According to Gerlach, 1 a clay containing 0.1 per cent, sulphate 

 of lime, which is the same as 0.4 grains per pound, would need 

 0.6 of a grain of barium carbonate per pound of clay. For safety, 

 however, 6 or 7 grains should be added to every pound of clay. 

 This would be about 100 pounds for every thousand bricks, based 

 on the supposition that a green brick weighs 7 pounds. As a 

 pound of barium carbonate costs about two and one-half cents, 

 the amount of it required for 1,000 bricks would be $2.50. It 

 is cheaper to use barium chloride, for the reason that the salt is 

 soluble in water, and hence can be distributed more evenly with 

 the use of a smaller quantity; the chemical reaction also takes 

 place much more rapidly when it is used. There is this objection 

 to it, however, that as near the theoretic amount as possible must 

 be used, for if any remains in the clay unchanged, that is, with- 

 out having reacted with the soluble salts, it may of itself form 

 an incrustation. 



In the case of a clay containing 0.1 per cent, calcium sulphate, 

 it would require 26 pounds of barium chloride per thousand 

 bricks, and this, at two and one-half cents a pound, would mean 

 an outlay of $0.65. With the barium chloride treatment, chloride 

 of lime is formed, but this is decomposed in burning. 



1 The Brickbuilder, 1898, p. 59 et seq. 



