256 Dr Hollis, Note on the Pulverization of 



two samples detailed elsewhere should be entirely due to this 

 small excess of impurity in the nickel-grains. 



Nickel shot when submitted to the action of a thin layer of 

 fuming nitric acid in the manner already described in my former 

 note proved to be less readily affected than the nickel-grains. 

 However by prolonging the exposure of the shot to the acid for a 

 period of more than a week I succeeded in obtaining definite 

 evidence of pulverization. The modus operandi was as follows : — 

 Two glass dishes were provided and the shot were submitted to 

 the action of the acid in one of these vessels until a dark green 

 discoloration of the liquid had ensued ; they were then transferred 

 to the other vessel and the process repeated. This operation was 

 continued at intervals so long as it was deemed necessary. Mean- 

 while the green liquid containing a small quantity of a black 

 powdery precipitate was freely diluted and the powder allowed 

 to subside. After numerous washings the powder (or what was 

 left of it) mixed with a few drops of water was placed by means 

 of a pipette upon a piece of thin sheet nickel and allowed to dry. 

 If the powder is permitted to dry in a glass vessel it adheres to 

 the surface so closely that its subsequent removal is rendered 

 difficult. 



The powder so obtained is about the colour and consistency of 

 lampblack. It is not pyrophorous, but is slightly hygroscopic. 

 Owing to its granular fineness probably, it smears readily on 

 paper. Its greasy or tarry nature is not diminished by soakage 

 in methylic alcohol and subsequently in ether. Whilst the specific 

 gravity of the powder is undoubtedly higher than water, thin 

 detached films often float upon the surface, and render the process 

 of washing the precipitate in my hands a wasteful and tedious 

 ordeal. When nickel shot have been exposed to the action of the 

 acid for some hours minute flakes of bright metallic lustre are 

 found commingled with the black powdery precipitate. If the 

 surface of a shot is examined after removal from the acid bath in 

 such a case, many superficial erosions are visible, mostly mapped 

 out by thin lines of black powder; here and there the surface 

 layers of the metal are so extensively undermined that a shot 

 not infrequently resembles a miniature onion with its outer coats 

 partly removed. The thinned free edges of these scales readily 

 break off; and form the flakes visible in the washings above 

 referred to. They are highly magnetic. The source of the black 

 adhesive powder cannot be so easily traced. That this substance 

 represents in some way the cement that welds the thin concentric 

 metallic layers of a shot into a homogeneous whole seems probable. 

 I must however leave its complete analysis to more competent 

 hands than my own. 



Thin Plates. The second sample forwarded me by the Mond 



