376 Count de Bournon on BardlgUone, 



tutes bardlgllone. Plaster, which is the result of the calcination of 

 gypsum, would then be bardiglione, which is far from being true. 

 The distinctive property of gypsum, when changed to the state of 

 plaster, is rapidly to absorb water, and, by that absorption, to acquire 

 consistency, and even a certain degree of hardness. Bardiglione, 

 neither before nor after calcination, has any action whatever on water; 

 and if reduced to powder before it is mixed with it, its particles still 

 retain their state of division. 



It is certain, therefore, that bardiglione and plaster, though com- 

 posed of the same principles, lime and sulphuric acid, and in the 

 same proportions, are two substances of different natures. And as 

 this difterence cannot arise from the nature of the principles entering 

 into combination, or from the manner in which they are proportioned 

 to each other, it must necessarily arise from the mode of arrangement 

 of the constituent molecules which form the integrant molecules. 

 Directing our view to this point, we shall see that gypsum, in its 

 transition to the state of plaster, having been deprived only of its 

 water of composition, without the combination of sulphuric acid 

 with the lime having been destroyed, each of the integrant molecules, 

 which compose the mass of plaster, should be considered as a right 

 trihedral prism, having scalene triangles for its base, perfectly similar 

 to the integrant molecules of gypsum, and exactly the half of its 

 primitive crystal'; but having void spaces, wltlrm the solid, similar in 

 shape to the molecule or molecules of water removed, the figure of 

 which is yet unknown to us. Thus the component particles of lime 

 and sulphuric acid are not in immediate contact in the integrant 

 molecules of plaster, except in parts of their surface ; while in bar- 

 diglione, on the contrary, these same component molecules are in 

 that state of approximation which is adapted to their complete 

 solidity. 



