THE ACIDS 



2, 



artificially from oil of vitriol and chalk or lime (p. n), 

 was called SULPHATE OF LIME. EPSOM SALTS, a purgative 

 salt derived from mineral springs, was shown by Black in 

 J755 to contain a base MAGNESIA in combination with oil 

 of vitriol ; it was therefore called SULPHATE OF MAGNESIA. 



Nitres or nitrates. NITRE or SALTPETRE (Fig. 

 p. 4), for many centuries 

 the only source from which 

 nitric acid and the nitrates 

 could be derived, was pre- 

 pared artificially in 1674 

 by John Mayow, a friend 

 and contemporary of 

 Boyle, by recombining the 

 nitric acid with potash ; 

 its systematic name was 

 therefore NITRATE OF 



POTASH. A NITRATE OF 



SODA was prepared by 

 Geber ; enormous deposits 

 of this salt have been 

 discovered in the desert 

 regions of Chile, and mil- 

 lions of tons are now ex- 

 ported every year for use 

 in agriculture under the 

 name of CHILE SALTPETRE. 

 The nitrates of the metals 

 were well-known to the 

 Alchemists. Geber describes LUNAR CAUSTIC, the NITRATE 

 OF SILVER, as prepared in the form of " small fusible stones 

 like crystal," by dissolving silver in aqua fortis and boiling 

 away two-thirds of the water in a long-necked flask. The 

 nitrates of lead, copper, iron, and mercury, were also prepared 

 at an early date. 



c 2 



FIG. 10 LARGE CRYSTAL OK GYPSUM OR 

 SELENITE (Sulphate of Lime). 



