78 NICKEL MINEEALS TKOM NEW CALEDONIA, 



The iron is present in tlie form of protoxide. 



After trial of all the methods of determining nickel in the 

 presence of alumina, iron, silica, and magnesia, it was found that 

 the best results were obtained by the process of first removing 

 the iron and alumina, converting the nickel into acetate, and 

 rapidly passing sulphuretted hydrogen to saturation. After 

 standing for a few hours the supernatant liquid would be 

 perfectly clear and bright ; if left standing many hours it Avas 

 often found that a portion of the nickel had again entered into 

 solution — at once detected by the blackening of the filtrate on 

 proceeding to wash the precipitate in the usual way with 

 sulphuretted hydrogen water. 



On comparing the physical properties and the chemical 

 compositions of these two varieties of nickel and magnesium 

 silicate with those of such minerals as Alipite, Pimelite, Grenthite, 

 and others, it will at once be seen that they bear certain 

 resemblances to one another ; but they do not possess sufficient 

 properties in common to group them under one name. 



From the following table comparing the different hydrated 

 nickel and magnesium silicates, it will be seen that although Alipite, 

 Garnierite, and Rewdanskite all are amorphous, have a green 

 coloiu', a hardness of about 2 to 2" 5, a low sp. gr. from 1"4 to 

 277, and adhere to the tongue, yet Grarnierite differs widely from 

 Alipite in containing far less magnesia, and from Rewdanskite 

 also in haAdng only 166 iron and alumina oxides against some 

 15 "40 per cent, entering into the composition of the latter. 



Then the three, Pimelite, Noume'ite, and G-enthite, besides 

 possessing several other physical characteristics in common, are 

 naturally still further bound together by the property which they 

 present of being more or less unctuous or greasy to the touch ; 

 yet in spite of these common properties they differ considerably 

 in chemical composition. 



Noumeite only contains from "509 to 3"00 per cent, iron and 

 aluminium oxides ; Pimelite, on the contrary, contains from 9"58 

 to 2573 per cent. ; and Genthite from 0"21 to 10"65 ; and more- 

 over, they differ much in their proportions of magnesia, water, and 

 other constituents. 



