332 SALTS -SULPHATES 



2. PROPERTIES. 



(a.) Crystals four sided prisms, with quadrangular pyramids, 

 having dihedral summits.* 



The prismatic form, according to Mr. Brooke, is a right rhom- 

 boidal prism, of 90 30, and 89 30. 



(b.) The Epsom salt of the shops is in the form of confused needle 

 like crystals. 



(c.) When pure, unchanged in the air; but sometimes deliques- 

 cent, from mixture with the muriate. 



(d.) Suffers aqueous fusion at low redness ; and loses about half 

 its weight, but is not volatilized, except a little of the acid. 



(e.) Soluble at 60, in 1 part of water, in f of its weight at 212, 

 the water is expanded J. 



(/.) Solution precipitated by carbonates ofpotassa and soda, (see 

 those articles.) Equal weights of the salts, in equal weights of boil- 

 ing hot water ; or, crystallized sulphate 4 parts, carbonate of potassa 

 3 parts, in solution ; 100 grains dry sulphate give about 71 carbonate 

 of magnesia, or 33. pure earth. 



(g.) The carbonate is, in this case, preferable to the bi-carbonate 

 of an alkali, because abundance of carbonic acid suspends the mag- 

 nesia ; heat would however, eventually throw down a precipitate. 



(h.) Carbonate of ammonia does not precipitate the earth, unless 

 heat is applied. 



(i.) Barytic, strontitic, and lime water throw down a mixed pre- 

 cipitate of carbonate of magnesia and a sulphate of the other earth. 



(y.) Decomposed by charcoal at ignition ; producing a sulphuret, 

 which is, however, feeble in its properties. 



(&.) Jit a high heat completely fusible, but without decomposition. 



(I.) Taste bitter, but less disgusting than that of sulphate of soda. 



(m.) JLn excellent cathartic; dose, 6 or 8 drachms, dissolved in 

 water; and, by many, preferred to Glauber's salts. 



3. COMPOSITION. 1 proportion of magnesia 20 33.04 



1 sulphuric acid, 40 66.96 



its equivalent number, 60 100.00 



The crystals contain, 



Magnesia, 16. or 1 proper. 20 

 Acid, 32.57 or 1 " 40 

 Water, 51.43 or 7 " 63 



100.00 123 the equivalent for the 



crystals. 



* For some varieties of the crystals, see Henry, Vol. I, p. 621. 



