SALTS SULPHATES. 333 



(a.) With pure ammonia, a part of the earth is precipitated ; by 

 evaporation a triple salt, called the amrnoniaco-raagnesian sulphate, 

 is obtained, consisting of 



Sulphate of magnesia, 1 proportion 60 



Sulphate of ammonia, 1 " 57 



Water, 7 " 63 



180 its equivalent number. 



(b.) Ji compound sulphate of magnesia and soda is obtained, by 

 evaporating the bittern of sea water ; it crystallizes in transparent 

 rhombs, and consists, according to Dr. Murray's analysis, of sul- 

 phate of magnesia 32, sulphate of soda 39, and water 29 ; and its 

 proportions are very nearly those of 1 equivalent of sulphate of mag- 

 nesia 60, 1 of sulphate of soda 72, and 6 of water, 54=186 for its 

 equivalent number. It is a cathartic, not disagreeable to the taste, 

 and is sold at Lymington, England.* 



(c.) A sulphate of potassa and magnesiaf is obtained, when 1 

 equivalent of sulphate of magnesia and 1 of sulphate of potassa are 

 mixed ; they crystallize with 6 of water, and there is a double salt 

 of 1 equivalent of sulphate of magnesia, and 1 of sulphate of ammo- 

 nia, with 8 of water, which is obtained by spontaneous evaporation 

 of the mixed solutions. 



4. ORIGIN OF SULPHATE OF MAGNESIA. 



(a.) Found abundantly in sea water, ancf obtained from the bit- 

 tern, after the evaporation for crystallizing common salt ; it is boiled 

 down, until, on cooling, in clear and cold weather, it affords the sul- 

 phate of magnesia, in acicular crystals, in the proportion of 4 or 5 

 parts to 100 of common salt, obtained from the same water; or sul- 

 phate of iron is added, to decompose the muriate of magnesia, and 

 thus increase the quantity of sulphate. J 



(b.) Manufactured from magnesian minerals, especially the mag- 

 nesite ; 1.500,000 Ibs. are made annually in Baltimore, from a mag- 

 nesite found near Chester, Penn. 



(c.) Found native and crystallized, in remarkable quantity, in a 

 great cave, at Corydon, Indiana ; also in many other limestone cav- 

 erns, in Kentucky, Virginia, and Tennessee, &c. 



(d.) Effloresces occasionally on brick walls. 



(e.) Formed by the decomposition of rocks, which contain mag- 

 nesia, and sulphuret of iron ; the latter affords the sulphuric acid, 

 which combines with the magnesia, and effloresces, and is extracted 

 by a process, for which see Thenard, 5th Ed. Vol. Ill, p. 169. 



* Murray, 6th Ed. Vol. II, p. 94, and Edinburgh Trans. 



t See Phil. Trans. 1822, p. 455, also Henry, 10th Ed. Vol. I. p. 625. 



t See muriate of magnesia. 



Am. Jour. Vol. XIV, p. 10. See also Vol. IV, p. 22. 



