300 Intelligence and Miscellaneous Articles. 



fectly decided, and cannot be confounded with the total loss, which 

 varies from 20 to 22 per cent, and corresponds to two equivalents of 

 water. The following are the results of experiments : — 



Artificial sulphate of lime, prepared by precipitating cold solutions 

 of sulphate of zinc and chloride of calcium ; when dried over sulphuric 

 acid the result was invariable. By exposure for six hours to a tem- 

 perature of 176° to 185° F. it lost 17 per cent. ; no further loss oc- 

 curred by exposure for an additional hour to the same temperature ; 

 when rendered perfectly anhydrous the loss was 22 per cent. 



Artificial sulphate of lime, precipitated from mixed boiling solutions 

 of sulphate of zinc and chloride of calcium ; dried as before, the loss 

 at 176° to 185° F. remained invariably at 15' 71 per cent. ; when 

 rendered anhydrous the loss was 20'87 per cent. 



Moistened plaster lost at the above temperatures 16'22 per cent. ; 

 rendered anhydrous, the loss was 20'39 per cent. 



Precipitated sulphate of lime, dissolved in hydrochloric acid, and 

 crystallized from it. — By fifteen hours' exposure to 176° up to 185°, 

 it lost no weight, and none occurred till the temperature reached 

 221° F., when it lost 15'38 percent. The same heat was afterwards 

 continued during four hours without further loss. Rendered anhy- 

 drous, the loss was 20'78 per cent. 



Arrow-headed gypsum from Montmartre. — This suffered no loss at 

 176° to 185° F. ; at 221° it amounted to 15-37 per cent., and the 

 total loss was 20' 78 per cent. 



Fibrous stilphate of lime. — In fifteen hours lost no weight at 1 85°F.; 

 at 221° the loss was 17'60 per cent. ; it was afterwards exposed for 

 twelve hours to the same temperature with scarcely any diminution ; 

 the total loss was 22'62 per cent. 



Alabaster from Volterra. — SuiFered no diminution of weight by 

 exposure at 176° to 185° F. ; at 230° F. the loss was 15-61 per 

 cent. ; several hours' continued application of the same heat occasioned 

 no further diminution of weight; the total loss was 20-83 per cent. 



Snow-white gypsum (Gypse en niege). — Lost no weight at 185° F.; 

 at 238° F. it was 15-57 per cent. No further diminution occurred 

 by several hours' longer exposure to this heat. The total loss was 

 21-27 per cent. 



Fibrous gypsum from America. — Lost no weight at 185° F.; at 

 230° F. lost 15-41 per cent. ; total loss 20-59 per cent. 



Prismatic gypsum from Sicily. — No diminution of weight atl85°F.; 

 at 230° it was 15-58 per cent., and the total loss was 20-44 per cent. 



It appears, therefore, that all native sulphates of lime retain their 

 water at 185° F., and do not lose any below 221° to 236°. Artificial 

 sulphate of lime crystallized in hydrochloric acid is similarly circum- 

 stanced. Artificial sulphate of lime, on the other hand, Avhether 

 precipitated hot or cold, loses three-fourths of the water at 176° to 

 185°. Moistened plaster is also dehydrated at this lower tempera- 

 ture. 



It will be obsen'ed that all the sulphates of lime undergo a frac- 

 tional loss of water, and that the second state of hydration is ex- 

 pressed by (S03)SHO-h2CaO. 



