Count DE BouRKON on BardigUone, 375 



them, but does not affect, In any degree, the essence of the sub- 

 stance containing it; this is water of crystallization in the true sense 

 of that term. But it happens not unfrequentjy that water enters as an 

 essential part or principle into the formation of their integrant mole- 

 cule, in which case it is not water of crystallization but water of 

 composition, and ought so to be denominated. It is obvious, that 

 the one does not necessarily exclude the other, for they are totally 

 unconnected with each other. It is obvious too, that we cannot 

 consider the water, which a substance may contain, as making 

 one of its component principles, unless there be solid reasons for 

 such a conclusion. For instance, in the case in question, the combi- 

 nation of lime with sulphuric acid gives rise to rectangular tetra- 

 hedral prismatic molecules with square or rectangular bases ; while 

 water, uniting with the same principles, combined In the same pro- 

 portion, gives rise to molecules in right tetrahedral prisms ,with rhom- 

 boidal bases, having angles of 113° 4' and GQ'^ 56' ; it is very evident, 

 that this water, by its union, has totally changed the form of the 

 integrant molecule, which it could only do by combining with it. 

 This fact will be rendered still more evident by what follows. 



Calcined gypsum then, from what has been shewn, must have 

 lost its water of composition. This loss must be owing to the 

 molecules of water having a much greater affinity for caloric in 

 motion, or heat, than It has for the other component molecules of 

 gypsum. 



If the gypsum had lost In calcination only Its water of crystalli- 

 zation, or, what comes to the same thing, that which was regularly 

 interposed between Its molecules, there would remain a simple com- 

 bination of lime and sulphuric acid, In the proportion of 32 parts of 

 lime and 46 of acid in every 78 parts, or 40 of lime and 60 of acid 

 in 100 ; a combination precisely the same with that which consti- 



