376 Theory of Cryjlall'tfaiion. 



ference is, that fait is added to the clay ufed for the alcarrazas, 

 and that they are only half baked. 



There is not a fingle family in Madrid where thefe veffels 

 are not ufed. They are filled with water, which is expofed 

 for feveral hours to a current of air, in order that the evapo- 

 ration may be more rapid, and that the water confequently 

 may become cooler. 



A kind of red veffels called bucaros, employed likewife to 

 cool water, are made alfo at a place called Salvatierra in 

 Eflramadura ; but the earth being lefs porous, it is not fo 

 proper for the intended purpofe. Befides, thefe vafes com- 

 municate to the water a difagreeable argillaceous tafte. 

 They are, however, in great requeft among the ladies of 

 Madrid ; fome of whom pound fragments of them, and mix 

 the powder with fnuff. Young girls have a particular fond- 

 ncfs for this kind of pottery, and eat it when they are 

 troubled with the chlorous. 



Vafes of a fimilar kind to thofe above defcribed, are em- 

 ployed in Portugal for moiftening fnuff. They are plunged 

 into water, after being filled with this article ; and the 

 water which filters infenfibly through them communicates 

 to it, at the end of fome hours, the neceffary degree of 

 humidity. 



VIII. On the Theory of the Struclure of Cryjlals, by the Abhji 

 TIaut, From Vol, XVII. of the Annales de Chimie, 



[Concluded from p. 303.] 

 III. Number of primitive Forms. 



JL N the examples before mentioned I have chofen a paral- 

 lelopipedon for nucleus, on account of the fimplicity of its 

 form, I have hitherto found that all the primitive forms 

 may be reduced to fix, viz. the parallelopipedon, in general, 

 iyv T hich comprehends the cube, the rhomboid., and all the 



