54 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



NOX-AMALGAMABLE GOLD. 



The attention of Mr. Skey, of the Geological Survey of 

 New Zealand, was called to a reported loss of gold during 

 the process of extraction by mercury, and he found, on care- 

 ful examination, that numerous samples of bright, clean-look- 

 ing gold of two degrees of fineness refused to amalgamate on 

 any part of their natural surfaces, and he ascertained by ex- 

 periment that on such surfaces sulphur- is always present. 

 He also found that native pure gold will readily absorb sul- 

 phur from moist sulphuret of hydrogen or sulphide of ammo- 

 nium, and that surfaces so treated refuse to amalgamate, al-' 

 though exhibiting no aj)parent change in their surfaces. He 

 shows, however, that by roasting in an open fire, or by bring- 

 ing it in contact with cyanide of potassium, chromic and ni- 

 tric acid, and chloride of lime acidified, gold so affected is 

 rendered amalgamable, unless copper be present to the ex- 

 tent of seven per cent., or perhaps less. 1 A, 1870, 282. 



THIRD SILVER ALLOY. 



An alloy, known as the Alliage tiers argent, or third silver 

 alloy, has been assayed, and has been ascertained to be com- 

 posed of copper, 59.06 parts ; silver, 27.56 ; zinc, 9.57 ; nickel, 

 3.44, making a total of 99.63 parts. Its external color is pre- 

 cisely similar to that of pure silver, but on the fracture, which 

 is finely granular, the color is light yellow, with a shade into 

 reddish. 13 C, August 11,1222. 



TESTING SILVERY COATING OF METALS. 



It is sometimes a matter of interest to be able to determine, 

 by means of a simple test, the nature of a silvery coating to 

 a metal, whether it be pure silver or some other substance. 

 This is said to be readily accomplished by the use of a cold 

 saturated solution of bichromate of potash in pure nitric acid, 

 of one and two tenths specific gravity. The- surface of the 

 article to be tested is to be first washed with strong alcohol, 

 so as to remove any lacquering, and then a drop of the solu- 

 tion applied by means of a glass rod, the place affected being 

 immediately after rinsed oft* with water. If the substance in 

 question be silver, a distinct blood-red spot of chromate of 

 silver will be perceived. The spot is brown on German sil- 



