SALTS SULPHATES. 327 



(/.) Insipid and harmless ; sp. gr. of the native salt about 2.26 to 

 2.31. 



3. COMPOSITION. According to Dalton, 58.60 acid, 41. 40 base. 

 Berzelius and Thomson 58. and 42. Dr. Henry thinks its true con- 

 stitution is, Acid, 58.42, or 1 proportion, - - = 40 

 Lime, 41. 58, or 1 " - -28 



100.00 68 



Crystallized sulphate of lime is composed of, 

 Sulphate of lime, 79.07, or 1 proportion, (anhydrous,) 68 

 Water, - 20.93, or 2 " 18 



100.00 86 



4. USES AND MISCELLANEOUS REMARKS. 



(a.) The native salt is abundant, in the form of alabaster, gypsum, 

 or plaster stone, selenite crystals, &c. Found in the ashes of vege- 

 tables, in the sea, and in many natural waters ; producing incrusta- 

 tions upon the pans of the salt boilers.* 



There is a native variety without water, called the anhydrite, but 

 it is rare, and its properties are different from those of the common 

 kind.f 



Sb.) Heated, it loses weight .22, and if in a retort, water may be 

 ected. 



(c.) Exhibits a false appearance of boiling, in consequence of the 

 escape of the water ; this is best shewn in a glass retort, with the la- 

 mellated variety ; it may be seen in a crucible with a forge heat. 



(d.) Thus prepared for statuary and stucco work. Heat the plas- 

 ter thoroughly, pulverize it fine, mix with a little good quick lime in 

 fine powder, and form into a paste with water. 



(e.) To copy a medal or coin, pour the paste into a box, oil the 

 surface of the medal to prevent adhesion, and brush it over with the 

 cream of the plaster to prevent air holes ; then impress it upon the 

 paste and let it harden. 



(f.) To copy a face, living or dead, or a statue ; the process is 

 the same, only laying the figure on a table, oiling the surface, and if a 

 living person, putting paper tubes in the nostrils, tying the hair back, 

 and pouring on the plaster of the consistence of a thick cream. The 

 muscles are kept composed, and in about 20 minutes, the cast will 

 grow firm, when it is removed. After forming the concave copy, the 

 convex is cast in it, and any mistakes are corrected or additions made ; 

 then a new concave is made upon this and serves as a permanent 

 mould ; statues are cast in parts and then joined. For stucco work, 



* And in the boilers of the steam boats, that use salt water. 



t It is found to be much more common than was formerly supposed. 



