Chap. 5.] Vitriolated Tartar. 23 



which have generally fix fides, four principal, and two 

 which feem accidental. Its cryftals, containing a large 

 quantity of water, are liable to have it abftracled from 

 them by the atmofphere, when they fall to powder, 

 or in chemical language efflorefce. How much water 

 Glauber's fait is capable of containing, is known by 

 its requiring twice its weight of water to cryftaliize. 

 The water fhould be added in a boiling Hate, and the 

 mixture boiled a little afterwards j it may be fet by 

 in a quiet place, and will be found cryftallized the 

 next day, or will fuddenly affume that ftate on being 

 fliaken. On cryftallizing, a quantity of heat is per- 

 ceived to be emitted by the fubftance paffing from a 

 fluid to a folid ftate, and confequently lofing fome of 

 its latent heat. 



Of Glauber's fait, all that is ufed at prefent is pro- 

 duced by art. It is faid to be produced by nature in 

 the waters of mineral fprings, and of the fea. But 

 the fait found * in them is ufually not Glauber's fait, 

 but Epfom fait, confifting of the vitriolic acid and 

 magnefia. Glauber's fait is obtained by uniting the 

 vitriolic acid with the mineral alkali of common fait, 

 as happens in the procefs for obtaining the muriatic 

 acid. 



VITRIOLATED TARTAR is diftinguifhed from Glau- 

 ber's fait, by a lefs degree of fufibility. It requires 

 for its fufion the ftrongeft fire. Its cryftals are harder, 

 but lefs bright, and do not contain fo much water as 

 thofe of Glauber's fait. Hence they are not liable 

 either to fpontaneous efflorefcence, nor to watry fu- 

 fion, but, like other falts, which contain little water, 

 attract it ftrongly. This fait decrepitates* in the 



* In decrepitation the cryftals burft, and fall into powder, from 

 the expanfion of the water which they contain, by the heat. This 

 occafions that crackling noife yvhich common fah makes when 

 thrown into the fire. 



C 4 fire. 



