164 PROCEEDINGS OP SECTION B. 



perceptibly darkened, and this is rendered nioi"e apparent by 

 comparing it with gold not sulphurized. Occasionally I have 

 succeeded in giving an irridescent appearance to it by this means. 



Gold thus treated affords a good reaction of sulphur, and is not 

 brought back to its original colour by hot hydrochloric acid, 

 from which I conclude that the dark film is composed of anhydrous 

 sulphide of gold. 



I should state that strips of jilatinum were digested alongside 

 these pieces of gold, and for an equally long time, but did not 

 manifest any change of colour. 



In this connection I may mention .that although platinum does 

 not darken in sulphide solutions, it is, however, aftected by them 

 as well as by sulphuretted hydrogen, becoming non-amalgamable. 

 Like gold, it is I'endered amalgamable by a short contact with 

 nascent hydrogen ; but unlike gold, it is rendered amalgamable by 

 cyanide of potassium. 



Platinum, however, becomes readily amalgamable on being 

 raised to a temperature of 400° to 600'^ F., also by a short contact 

 with any of the foUowiug substances : — Chromic acid, nitric acid, 

 or chlorine, but sulphuric and hydrochloric acid do not have this 

 eifect. 



It further appears that platinvim is also brought into a non- 

 amalgamable condition by a short contact with an aqueous 

 solution of potash or ammonia ; in these cases, however, the 

 application of hydrochloric or sulphuric acid renders it readily 

 amalgamable. In none of these cases did the metal appear to 

 sustain any visible change upon its surfaces. 



The results tlms stated tend to show : — 



First. — That platinum, like gold, is capable of absorbing 

 sulphur at common temperature, either from a solid 

 or gaseous compound. 

 Second. — That this absorption is chemical. 

 Third. — That this metal is superficially oxydized in alkaline 

 solutions. 



These results, as I have said, appear to impugn the correctness 

 of the opinion, that gaseous absorption by platinum is, in every 

 case, simply mechanical. 



There is another and suggestive fact to record here, namely — 

 that dry sulphuretted hydrogen does not aflect platinum, water 

 being necessary to assist the reaction. It is probable, therefore, 

 that in the cases where I sulphurized gold, water was also 

 necessary. What part it plays in the reaction does not readily 

 appear from wliat is known of the properties of gold. My 

 observations in the next section of this paper may throAv some 

 light on this subject. 



I think I have furnished sufficient evidence to show that the 

 absorption of sulphur by gold is chemical, but a§ I am desirous of 

 getting all the evidence possible, I have endeavoured to get those 



