70 AMALGAMS. 



ceases, and the acid begins to evaporate. The sulphate 

 of silver which is produced is then dissolved in the 

 requisite quantity of hot water, and the solution de- 

 canted from the gold, which, for greater certainty, is 

 once more heated with a small quantity of sulphuric 

 acid ; afterwards thoroughly washed, ignited, and 

 weighed. 



Y. All such alloys may be also conveniently ana- 

 lyzed by fusion with bisulphate of potassa. 



45. AMALGAMS. 



The following amalgams may be analyzed by heating 

 very gradually in a porcelain crucible, finally raising 

 the heat to redness, till the mercury is entirely vola- 

 tilized, and the tin or copper oxidized. To insure 

 complete oxidation, the mass is ultimately moistened 

 with concentrated nitric acid, and again ignited. The 

 amalgam of silver leaves the latter in the metallic state. 

 In order to estimate the mercury also directly, the fol- 

 lowing method is adopted : 



I. AMALGAM OF COPPER.* The amalgam is dis- 

 solved in aqua regia, the solution neutralized, though 

 not completely, with potassa, mixed with formate or 

 sulphite of potassa or soda, and allowed to stand for 

 some time at a temperature between 50 and 60. All 

 the mercury is thus precipitated as subchloride. 

 Above 60, metallic mercury would also be separated. 

 The subchloride of mercury is collected upon a filter, 



* Tins amalgam, which is semi-fluid at 100O,but solid and crys- 

 talline at the ordinary temperature, is obtained when copper, 

 which has been precipitated by zinc, is moistened with nitrate of 

 suboxide of mercury, and triturated in a warm mortar with mer- 

 cury, added by degrees, until the amalgam has the consistence of 

 butter. 



