"Nickel-grains" in Fuming Nitric Acid. 255 



angular in shape 1 . The powder dissolves in fuming nitric acid 

 to some extent. Here again certain grains apparently assume 

 the passive state and are not affected by the acid. The solution 

 acquires the well-known green colour of nickel nitrate. The 

 powder therefore so far behaves as the massive metal under like 

 conditions. 



The ductile and tenacious nickel observable in the wire and 

 sheet of commerce suggests a fibrous structure. On the other 

 hand nickel-grains, apart from other considerations, in their mere 

 brittleness and in the appearance of the fractured surfaces in- 

 dicate a crystalline texture. Now ductile fibrous nickel can be 

 made into a permanent magnet, specially is this true of the wire ; 

 and in spite of its sheen the wire shows "passivity" in the 

 presence of fuming HN0 3 . On the other hand nickel-grains, 

 although they are magnetic inasmuch as they attract the poles 

 of a compass needle, do not show sufficient polarity in my 

 experience to repel them. Moreover they do not constantly 

 show passivity when introduced into fuming nitric acid, even 

 when visibly coated with the oxide. In my opinion the pas- 

 sive (2) and the critical (3) states of this metal are intimately 

 associated with its molecular arrangement. 



Since writing the preceding note " On the Pulverization of 

 ' Nickel-grains' in fuming Nitric Acid," I have had an opportunity 

 of examining, through the courtesy of the Managing Director, 

 Mr Carl Langer, two samples of nickel prepared by the Mond 

 Nickel Company. One of these samples consisted of a massive 

 variety of the metal, termed "shot"; the other specimen was 

 made up of three thin-walled tubes ; to be described hereafter. 



Mond Nickel shot. The metal in this case appeared as some- 

 what irregularly shaped balls, having a brilliant silvery lustre, 

 and weighing about a drachm each. Upon a close examination 

 of the surface of a shot the irregularities were found to be due 

 to an ill-defined polyhedral shape with outcropping solid angles. 

 The shot, I understand, contains Ni 99'5 °/ 2 . A recent sample 

 from Johnson, Matthey and Company, in the form of nickel- 

 grains, yielded 99 °/ of the pure metal ; this gives the Mond 

 nickel the advantage of half per cent, as regards purity over the 

 ordinary commercial nickel. To my mind it is almost incredible 

 that the differences observable in the physical characters of the 



1 I have roughly measured the angles of various nickel-grains. They are 

 approximately 72°, 90°, 120°, 145°. Other angles are observable but these in my 

 experience are the commonest. The angles italicized are frequently met with. 



2 Mr Langer kindly forwarded me the following analysis of the shot : — Ni 99 - 50 ; 

 Cu 0-03 ; Fe 0-29 ; S 0-02 ; Insol. O'll. 



17—2 



