56 PROCEEDINGS OF THE AMERICAN ACADEMY 



is then evaporated over the water-bath until it has become ahnost 

 entirely dry, — or until it no longer exhibits any tendency to effervesce ; 

 it is then somewhat more strongly heated on a sand-bath, until all the 

 free sulphuric acid has been driven off, that is, until fumes of sulphuric 

 acid are no longer perceptible. The necessity of thoroughly evapo- 

 rating this mixture cannot be too strongly insisted upon, for a solution 

 of gold in sulphuric acid * is formed when the mixed nitrates, etc. are 

 treated with sulphuric acid, and unless this compound be entirely 

 destroyed by heating, it will be subsequently decomposed when water 

 is added, and give rise to a precipitate of metallic gold, in a condition 

 so finely divided that it cannot be separated by filtering. The occur- 

 rence of this precipitate would ruin the analysis. We at first sought 

 to prevent the formation of this solution of gold in sulphuric acid, by 

 heating very strongly the residue left in the flask after all the nitrate 

 of ammonia had been decomposed, until the escape of nitrous fumes 

 had entirely ceased, and the nitrate of copper was decomposed. We 

 then treated the mass with pure dilute nitric acid, and filtered off the 

 solution from the gold which had been deposited and fi'om any chloride 

 of silver which had been dissolved by the nitrate of ammonia, with the 

 intention of determining the lead directly, by precipitating it as sul- 

 phate from this solution after evaporation with sulphuric acid. It was 

 found, however, that a large portion of the gold-salt escaped decom- 

 position in the flask, the yellow solution of sulphate of gold being 

 formed almost as abundantly after this treatment as when the flask 

 was not heated so strongly ; and since in this method there is great 

 risk of fracturing the vessel from drops of acid condensing in its neck 

 and flowing down upon the hot portion, it can in no wise be recom- 

 mended. A perfectly dry mixture of sulphate of copper, sulphate of 

 lead, and metallic gold having been obtained, it is treated with distilled 

 water, — a considerable quantity of the latter being added at once, and 

 the mixture quickly stirred to prevent the sulphate of copper from 

 forming a hard cake as it becomes hydrated. As soon as the sulphate 

 of copper is completely dissolved, a small quantity of pure sulphuric 

 acid is to be added to the solution, and the latter set aside for at least 

 forty-eight hours. The precipitate, consisting of sulphate of lead and 

 metallic gold, was then collected upon a small Swedish filter and 

 washed, first with dilute sulphuric acid to remove the sulphate of cop- 



* Compare Pelletier, Ann. Ch. et Phys. [2], XV. 12. 



