222 



Platinum rendered thus non-amalgamable, becomes again readily amalgam- 

 able at a temperature of 400° to 600° F., also by a short contact -with any 

 of the following substances at common temperatures, — chromic acid, nitric acid, 

 nascent hydrogen, or chlorine. 



Svilphuric and hydrochloric acids had not this effect, neither had cyanide of 

 potassium, not even when boiled with it. 



Upon the siu'faces of platinum thus treated with either of these sulphides, 

 sulphur was readily detected by digesting them in a boiling solution of cyanide 

 of potassium, and applying the nitro-prusside test. 



It further appeared that platinum is also brought into a non-amalgamable 

 condition by a short contact with either aqueous solution of potash or 

 ammonia ; even distilled water had the same effect if allowed contact for an 

 hour or two ; this may be owing, however, to traces of ammonia present in it. 



In these cases, however, the application of hydrochloric or sulphuric acid 

 to the platinum, rendered it readily amalgamable. 



Clean platinum has been found to amalgamate readily, after twenty-four 

 hours contact, with dry air. 



In none of these cases did the metal appear to sustain any visible change 

 upon its surfaces. 



The results thus stated, tend to show, — 



1st. That platinum, like gold, is capable of absorbing sulphur at common 

 temperature, from either a solid or gaseous compound of it. 



2nd. That this absorption is chemical. 



3rd. That this metal is superficially oxydized in alkaline solutions. 



These results, therefore, to a certain extent appear to impugn the correct- 

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

 simply mechanical. 



Art. XXXIX. — On the Capability of Certain Sulphides to form the Negative 

 Pole of a Galvanic Circuit or Battery. By W. Skey, Analyst to the 

 Geological Survey of New Zealand. 



[Read before the Wellington Philosoijhical Society, October 22, 1870.] 



When a piece of massive galena is placed in voltaic contact with amalgamated 

 zinc, and immersed along with it in weak sulphuric acid, to within an inch 

 or two of the point of contact, a galvanic current is at once established, gas 

 in quantity being given off at the surfaces of the galena, while the zinc is 

 rapidly oxydized. 



Three or four such pairs when connected among themselves, intensity 

 fashion, afford a current of electricity strong enough to decompose acidulated 

 water, and manifest all the phenomena of a small galvanic battery. Such an 



