380 M. C.Lea — Transformations of 



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

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

 ciency of the agate mortar. 



Silver Garhonate. — 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, fil- 

 tered 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 after treatment with 

 ammonia and cannot distinguish 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 decomposi- 

 tion product, the particles protect one another. And even 

 when all other things are equal the product will depend on the 

 activity and dexterity with which the grinding is done. 



But what is really important is that the amounts obtained 

 enable us in particular cases, to determine the exact amount of 

 mechanical energy which has been transformed. 



In concluding this paper, two cases will be mentioned which 

 do not belong to the above category, inasmuch as the reductions 

 are exothermic. As a general rule, to cause substances to part 

 with oxygen, energy must be supplied, but there are excep- 

 tions. Auric oxide, for example, disengages heat in parting 

 with oxygen and the same is the case with potassium perman- 

 ganate. 



