382 Transactions. — Chemistry. 



renders this oxidized gold amalgamable may be explained in 

 the same way ; while the inability of sulphuric acid, or the 

 iron-sulphate, to render gold amalgamable leads me to suppose 

 that a basic sulphate of gold forms on the metal when these 

 substances are used, and that this sulphate is not, or at least 

 is not readily, decomposed by the mercury, so the amalgama- 

 tion of the gold is much delayed or altogether impeded. This 

 explanation of the anomaly referred to seems feasible to any- 

 one who will compare this behaviour of gold with that of 

 silver under much the same circumstances. This metal (silver) 

 becomes rapidly non-amalgamable in distilled water, and, like 

 gold that has been in the same water, becomes easily amal- 

 gamable by contact with hydrochloric acid or a chloride, and 

 this solely, as we know, by a changing of the oxide or car- 

 bonate of silver that has formed in the distilled water into a 

 chloride, which salt is rapidly decomposed by mercury, and 

 so amalgamation readily proceeds. 



This appears to me a satisfactory explanation of the 

 anomaly described in my former paper, supposing that, as I 

 allege, the refusal of gold that has had contact with air and 

 water to amalgamate is really owing to its having been 

 superficially oxidized therein ; and that this is so I am now 

 enabled, by the use of my gold-test papers, to demonstrate 

 beyond all doubt. 



Now, as every chemist and photographer knows, most of 

 or all the compounds of gold with the other elements except 

 sulphur and its congeners are soluble in hyposulphite of soda. 

 This salt, therefore, in conjunction with air and water, should 

 dissolve (metallic) gold — that is, it should (if the gold is 

 oxidized under these circumstances) dissolve the oxide or 

 carbonate of gold formed thereon, and so ultimately take up 

 the whole of the gold present in my test-paper within a 

 reasonable time. 



Acting on this supposition I tried the experiment, and 

 found that if only the "hypo." is prevented from breaking 

 up into sulphide compounds the gold is all quite removed 

 from the paper in a few hours by the hypo. If we use 

 the hyposulphite alone there is no certainty of result, as it is 

 so easily decomposed to form a salt (sodic sulphide) that 

 produces sulphide of gold, a compound not soluble in the 

 hypo. By putting a little potash in the hypo, this decompo- 

 sition is prevented and the gold is always completely removed. 

 It was afterwards found that ammonia even has a solvent 

 effect upon metallic gold, but its action is considerably slower 

 than that of the hypo. Potash alone, it may be stated, did 

 not show any solvent power upon gold. 



That gold is, as shown above, soluble in hyposulphite of 

 soda, also in aqueous ammonia, proves beyond all doubt that 



