of the Metallic Oxides. 103 



is a yellow salt, known as turbith nitreiuc. By prolonged 

 treatment with water this salt becomes more and more basic. 

 Kane has described a salt having the composition Hg(N0 3 ) 2 . 

 5HgO. Finally it gives mercuric oxide. Nitrate of bismuth 

 behaves in a similar manner. A large quantity of w T ater, hot 

 or cold, converts mercuric sulphate, HgS0 4 , into trimercuric 

 sulphate, HgS0 4 . 2HgO, which, in the presence of an alka- 

 line solution, finally becomes mercuric oxide. The solution 

 of oxide of antimony in fuming sulphuric acid yields, accord- 

 ing to Peligot, the crystalline salt Sb 2 3 . 2S0 3 . The latter 

 in the presence of water gives the basic salt H 2 S0 4 . 2Sb 2 3 , 

 which completely decomposes in the presence of a large 

 quantity of water into oxide of antimony. Antimony trichlo- 

 ride, SbCl 3 , gives, when treated with water, white precipitates 

 of oxychlorides, which are finally converted into the oxide. 

 One of these compounds is crystalline, and has the formula 

 5Sb 2 3 . 2SbCl 3 . It is well known with what facility oxide 

 and chloride of mercury combine to form oxychlorides 

 (HgO) x . (HgCl 2 ) y . These can be obtained in different ways, 

 and are of very varied composition. Several of them are 

 crystalline, one of the latter being 6HgO . HgCl 2 . They are 

 all converted into mercuric oxide in alkaline solution. 



It is only natural to suppose that, when these various basic 

 compounds are converted, either by the action of water alone, 

 or in the presence of an alkali, into the oxide, with the total 

 elimination of the acid radical and its replacement by oxy- 

 gen, the bonds, which hold together the several radicals or 

 atoms of the metal in one and the same molecule, remain 

 throughout. The action of the water having originally de- 

 termined them, it would be illogical to suppose that at a 

 particular moment they cease to act. 



Acid Anhydrides. — The same reasoning may be applied to 

 anhydro-compounds produced by the action of strong acids 

 on their salts, and especially on their acid anhydrides, as in 

 the case of the chromates. 



Chromic anhydride, Cr0 3 , forms three series of salts : — 



Monochromates . K 2 O0 4 or K 2 . Cr0 3 . 

 Dichromates . . K 2 Cr 2 7 or K 2 . 2Cr0 3 . 

 Trichromates . . K 2 Cr 3 Oi or K 2 . 3Cr0 3 . 



Under the action of an acid, such as sulphuric, the mono- 

 chromate is converted successively into the di- and tri-chro- 

 mates, and finally into the anhydride. The latter ought, 

 therefore, to be represented by some multiple of Cr0 3 . 



Finally, we find a direct proof of this polymerization in the 

 decomposition of the arsenites by acids. Among these salts 



