effected by Mechanical Force. 353 



obtained. In all cases the material was wrapped in either 

 platinum- or silver-, usually platinum-, foil. There was no 

 action in any case on the metal, which preserved its full 

 brightness in the parts in contact with the material, so that 

 the effects observed were due to pressure only. 



Silver sulphite in platinum-foil was moderately darkened by 

 two days' pressure. 



Silver salicylate was rendered very dark by two days' 

 pressure. 



Silver carbonate was moderately darkened by a somewhat 

 longer pressure. 



Silver tartrate was not affected. 



Silver oxide was thoroughly dried at 150°. A piece of 

 platinum-foil was heated- to redness and rapidly cooled, a 

 portion of oxide was folded up in it and weighed. Weight found 

 •7639. It was then subjected to very great pressure for four 

 days. Weight found to be *7639 ; no change. 



Ferric oxide recently precipitated and dried. No effect 

 produced by pressure ; no formation of ferrous oxide. 



Potassium platinobromide. — Where the pressure was 

 greatest the brilliant red colour of this substance was black- 

 ened, not superficially only, but all through. 



Ammonium platinochloride. — Moderate but well-marked 

 darkening. 



Potassium chlorate. — When this substance was subjected to 

 pressure by itself, no effect whatever was produced, and not a 

 trace of chloride was formed. But when it was mixed with 

 silver nitrate, both in fine powder, and subjected to pressure 

 there was an evident formation of silver chloride. The 

 material was no longer completely soluble in water, but left 

 an abundance of white flakes which darkened when exposed 

 to light. 



Mercuric oxide requires a very high pressure to produce an 

 effect upon it. It then darkens slightly but very distinctly, 

 and this change seems to be accompanied by a slight loss of 

 weight, requiring, however, very careful weighing to detect 

 it. The darkened part, as well as the rest, dissolves without 

 difficulty in acetic acid, and consisted therefore probably of 

 traces of mercurous oxide and not metallic mercury. 



Mercurous chloride showed no change. 



Mercuric chloride. — Corrosive sublimate perfectly free from 

 calomel, which commercial sublimate is very apt to contain, 

 was subjected to great pressure and then treated with 

 ammonia. As no darkening took place, there had evidently 

 been no reduction. 



Mercuric iodide. — Red mercuric iodide, when subjected to 



