120 



ESSAY VI. 



lime, combined with acid of arsenic, be edulcorated, and 

 afterwards strongly calcined for an hour in a close crucible, 

 it will form a thick flux ; but it still retains the acid of 

 arsenic, (e) If it be mixed with the same quantity (in 

 measure) of charcoal powder, and exposed to a strong fire 

 in a retort, a shining regulus of arsenic will be sublimed. 

 The residuum is quicklime mixed with charcoal, still how- 

 ever containing some arsenic. 



SECTION XVI. UPON MAGNESIA. 



(a) Magnesia dissolves in acid of arsenic ; but when the 

 solution comes to the point of saturation, the mass coagulates. 

 This coagulum being dissolved in a larger quantity of acid of 

 arsenic, and evaporated, the solution grows gelatinous ; if the 

 jelly be lixiviated with water, filtered and evaporated, a 

 viscid mass remains, which will not crystallise, (b) The 

 solutions of magnesia in vitriolic, nitrous, muriatic, and 

 acetous acids are not precipitated by the acid of arsenic, 

 but very readily by the neutral arsenical salts (Sees. vi. (a), 

 vii. (a), VIIL (a)). The precipitate is easily soluble in acids, 

 but not in water. (c) Exposed to the fire in a crucible 

 with charcoal, it shows the same phenomena as the pre- 

 cipitate of lime (Sec. xv. (d), (e)). 



SECTION XVII. UPON EARTH OF ALUM. 



(a) The earth which is precipitated from a solution of 

 alum by alkali of tartar, after being washed with boiling 

 water, is easily soluble in the acid of arsenic, till it becomes 

 quite dry. The solution coagulates as soon as it arrives at 

 the point of saturation. (b) Dissolved in the vitriolic, 

 nitrous, and muriatic acids, it is not precipitated by the 



