1871.] Mercurial Colloids and certain Fatty Ketones, 437 



mercuric methide be formed during the rapid decomposition of the mer- 

 curic compound, the first step in the reaction by which it is produced 

 may be explained by the following equation : — 



[2CO(CH 3 ) 2 , 3HgO j= 2(^3 } Hg ) + Hg + 2C0 2 + ? 



The mercuric methide produced in the first instance, probably at another 

 stage suffers nearly complete decomposition in presence of the oxygen 

 liberated at the outset of the reaction. 



d. Chemical nature, of the Diaceto-mercuric Hydrate. — In the pre- 

 ceding section the properties of the colloid liquid and other bodies ob- 

 tained by dialysis from the potass solution have been described ; but the 

 potassium hydrate used in the first instance may be replaced by solution 

 of sodium, barium, or even calcium hydrate, and yet the same ultimate 

 result arrived at. When sodium hydrate is employed, no material dif- 

 ference is observed at any stage of the operations, but when barium 

 hydrate is substituted, re-solution of mercuric oxide in presence of acetone 

 is quickly effected with the aid of heat ; but this alkaline solution slowly 

 decomposes, yielding a white precipitate of the mercuric ketone com- 

 pound, mixed with a little barium carbonate. This decomposition takes 

 place in closed vessels, and most rapidly when the solution has been 

 boiled in course of preparation, and when no excess of barium hydrate 

 has been employed beyond the amount absolutely required to secure the 

 retention of the mercuric compound in solution. 



Keeping in view the peculiar mode of generation of the mercuric 

 ketone compound, its solubility in alkaline liquids at the time of its forma- 

 tion, and insolubility without decomposition in acid solutions, its power of 

 uniting with water to form both liquid and gelatinous hydrates, and the 

 extremely close analogy of these in properties and relations to the " co- 

 silicic acids" of Prof. Graham, we are compelled to attribute to the new 

 hydrates very feeble acid functions. 



The alkaline solutions above referred to may therefore be regarded as 

 containing metallic salts of a peculiar acid, derived from the compound 

 ((CH 3 ) 2 CO) 2 Hg 3 3 , already described. That these salts are, however, 

 even more easily decomposed than alkaline silicates is shown : — 



1st. By the easy decomposition of the potassium salt by the process 

 of liquid diffusion. The osmotic force alone is sufficient for this purpose, 

 the high diffusive energy of potassium hydrate enabling it to rapidly pass 

 through the dialytic septum, leaving behind the colloid acid in the liquid 

 state. The analogous decomposition occurs somewhat less readily in the 

 case of potassium silicate. 



2nd. By the facility with which the new acid may be displaced from 

 the aqueous solutions of its potassium, sodium, or barium salts by so 

 feeble an agent as carbonic acid. Solutions of alkaline silicates are well 

 known to decompose in the same manner, but less rapidly. 



