684 NEW YORK STATE MUSEUM 



immediate contact witli the soluble sulfates. While only a small 

 quantity of barium salt is required, still tO' insure thorough mixing, 

 10 to 20 times the necessary amount should be employed, and it 

 can be used without any injurious results. The following example 

 is given by Gerlach. The clay must first be ithoroughly analyzed 

 to determine the amount of sulfates. If, for example, the clay con- 

 tained .1/^ of sulfate of lime, this would mean that one pound con- 

 tained .4: of a gram, and theoretically every gram of sulfate of 

 lime needs 1.45 grams of barium carbonate to render it insoluble; 

 therefore theoretically a pound of clay would require .6 of a gram 

 of barium carbonate, or for safety six or seven gTams should be 

 used for every pound of clay. This would be about one hundred 

 pounds for every thousand bricks, based on the supposition that a 

 gTeen brick weighs seven pounds. As a pound of barium carbonate 

 costs 2^c, the amount of it required for a thousand brick would cost 

 $2.50. It is cheaper to use barium chlorid 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 takes 

 place much more quickly when the barium chlorid is used. There 

 is the objection to it that as near as possible the theoretic amount 

 must be used, for, if any of it remains in the clay, without reacting 

 with any sulfate, it will form an incrustation on the surface of the 

 brick. To give an example of the use of chlorid of barium, we may 

 take again a clay containing .1^ of calcium sulfate. This would 

 require theoretically 1.8 grams of crystallized barium chlorid and, 

 passing over the intermediate stages of the calculation, a thousand 

 bricks would require 57.4 kilograms of barium chlorid. If barium 

 cost 2^c a pound, a thousand brick would require an extra outlay 

 of only 32c, in using barium chlorid. Chlorid of lime is also 

 formed, but this has no injurious effect provided the clay is heated 

 to such a temperature as will cause the lime to unite with other 

 bases and silica, and form a complex silicate. If heated high 

 enough to decompose the chlorid of lime, it might be that its sub- 

 sequent slaking would be injurious. 



