Mechanical into Chemical Energy, 473 



produced immediate purple clouds in a cold, very dilute so- 

 lution of gold chloride and an abundant blue precipitate in 

 one of potassium ferricyanide. 



It is essential that the ferric alum be thoroughly dried (at 

 a temperature not exceeding 40° C), otherwise, owing to the 

 large quantity of water of crystallization, it will become pasty 

 in grinding and then no reduction will take place. 



Cupric Chloride. — Even by long trituration this salt showed 

 no indication of reduction. 



This reaction, taken with the preceding, shows how distinct 

 is the action of mechanical energy from that of heat. For 

 cupric chloride is reduced by heat to cuprous chloride, but 

 shearing-stress has no such action. On the other hand, 

 shearing-stress reduces ferric sulphate, which heat does not. 



Sodium Chloraurate. — In the previous paper, the effect of 

 triturating this salt in a porcelain mortar was given. For 

 comparison it has since been tried in an agate mortar. With 

 20 to 25 minutes' trituration, 3 decigrams gave 2*7 milligrams 

 metallic gold, showing, as in other cases, the much lower 

 efficiency of the agate mortar. 



Silver Carbonate. — Half a gram was triturated about 

 25 minutes in a porcelain mortar. It darkened much. The un- 

 altered carbonate was dissolved out by exhausting repeatedly 

 with ammonia. The residue was treated with nitric acid, 

 filtered, and the silver thrown down by hydrochloric acid. 

 It amounted to 11 milligrams, corresponding to metallic silver 



•0083. 



Silver Sulphite was precipitated in a dark room by alkaline 

 sulphite and treated in the same manner as the foregoing. 

 Silver chloride obtained *0092, corresponding to metallic 

 silver -0069. 



Silver compounds, although easily giving weighable results, 

 are not well suited for determining the transformation of 

 energy that takes place. It is probable that the reduction is 

 to argentous salt, but it is not certain. Ammonia decomposes 

 argentous salts into argentic salts that dissolve and metallic 

 silver that remains. So that whether we consider the reduc- 

 tion as being to argentous salt or to metal, in either case we 

 find the same quantity of metallic residue and cannot distin- 

 guish with certainty. 



It scarcely needs to be said that the object of these -various 

 determinations is not to establish any relation between the 

 quantity of substance taken and the amount of decomposition 

 that ensues, for none exists. It often happens that when a 

 larger quantity is taken there results a diminished decom- 



Phil. Mag. S. 5. Vol. 37. No, 228. May 1894. 2 K 



