170 ESSAY XII. 



the ignoble metals, the solution is of a bluish cast, (c) If 

 there be added to it a little alkali of tartar, the earth 

 becomes soluble in greater quantity in water, and after 

 evaporation shoots into small confused crystals. This small 

 quantity of alkali prevents the earth from being volatilised 

 in the open fire (Sec. vi. (&)). (d) This solution, while hot, 

 more clearly shows its acid property, and tinges lacmus of a 

 deeper red. It effervesces with chalk, with magnesia, and 

 with earth of alum, with which earths it forms neutral 

 salts, which are very difficult of solution in water, (e) 

 It precipitates silver, quicksilver, and lead dissolved in 

 nitrous acid, as also lead dissolved in marine acid. These 

 precipitates are reduced upon charcoal, and the melted 

 earth runs into the pores of the charcoal. The other 

 metals are not precipitated, nor is corrosive sublimate. (/) 

 It also precipitates the earth of the ponderous spar from 

 nitrous or marine acid. This precipitate is not a regenerated 

 spar, because it is soluble in cold water, a property which 

 regenerated ponderous spar does not possess ; the solutions 

 of other kinds of earth are not precipitated. (g) This 

 solution also expels the aerial acid from the fixed and 

 volatile alkalies, and forms with them neutral salts, which 

 precipitate all metallic solutions. Gold, corrosive sublimate, 

 zinc, and manganese are precipitated in the form of a white 

 powder ; iron and tin, from their solution in marine acid, of 

 a brown ; cobalt, of a rose colour ; copper, blue ; the solutions 

 of alum and quicklime, white. If the ammoniacal salt 

 formed by the earth of molybdsena and volatile alkali be 

 distilled, the earth parts with its alkali in a gentle heat, 

 and remains itself in the retort, in the form of a grey 

 powder. 



