324 



SCLPHURET OP LEAD, COPPER, AND AXTIMOKY. 



Objection. 



Answered. 



water, only in not containing of the last of these three 

 constituent principles. Yet this simple privation, by- 

 producing a substance of a different form, harder, heavier, 

 and possessing different chemical properties likewise, shows, 

 that water, which combines as a principle with lime and 

 sulphuric acid in the formation of gypsum, is necessary to 

 its formation, and that gypsum is consequently the result 

 of a real triple combination. 



It may be objected indeed, that in gypsum there exists 

 only a double combination between the molecules of sul- 

 phate of lime on the one hand, and those of water on 

 the other. But, if this were the case, when the water had 

 been expelled from the gypsum by calcination, the sul- 

 phuric acid being left, there should still be an intimate 

 combination between the molecules of the sulphuric acid 

 and those of the lime : and the plaster, which results from 

 this calcination, should exhibit a substance precisely of the 

 same nature as that known by the name of anhydrous 

 gypsum, or bardiglion (as I call it,) whereas in fact there 

 is no similitude whatever. The bardiglion reduced to 

 powder, either before or after calcination, possesses none of 

 the properties of gypsum, and does not absorb any water 

 whatever, so as to combine with it, and thus acquire the 

 solid form. By the great avidity with which calcined gyp. 

 sum seizes on water, the moment it comes into contact with 

 it, we discover that calcination, by taking from each of the 

 integrant molecules of gypsum (composed of those of 

 sulphuric acid, lime, and water) the molecules of water, 

 has changed the integrant molecules of this substance into 

 new molecules, consisting simply of those of lime and acid, 

 but having only an incomplete form : or, if I may be 

 allowed so to express myself, we perceive that this calcina- 

 tion has carried away a part of each of the integrant 

 molecules of gypsum, and left in each one or more cavities, 

 the sides of which, having a very powerful affinity for th« 

 corresponding sides of the molecules of water, seize on 

 them as soon as they have an opportunity of so doing, and 

 fix them again in the places to which they belong. Gypsum 

 is then in fact the result of a triple combination. 



But 



