501 



boiling at 203 C. This per-ccntage corresponds, however, to no 

 definite hydrate of simple atomic composition ; an acid having the 

 formula HC1G 4 -f 2(H 2 G) containing 73'63 per cent. II C1G 4 . 

 Aqueous perchloric acid follows, therefore, the same general rela- 

 tions respecting composition and boiling-point which I have shown 

 hold good for so many aqueous acids * ; namely, that the phenomena 

 of constant composition and fixed boiling-point are in the above cases 

 dependent mainly upon physical rather than upon chemical attrac- 

 tions. The specific gravity was found to be 1709 at 1 1 C. 



The reactions of aqueous perchloric acid have been sufficiently 

 studied by other observers. 



To the foregoing description of the properties of perchloric acid 

 and its hydrates, I have to add the following analyses of a few of the 

 salts of this acid which have hitherto not been examined. These 

 analyses serve to confirm the fact that the estimation of perchloric 

 acid by precipitation as potassium-salt in alcoholic solution is in 

 accuracy second to few of the most exact methods of quantitative 

 determination. 



(1) Perchlorate of Ammonium, NH 4 C1G 4 . 



This compound is one of the very few non-deliquescent salts of 

 perchloric acid. It is anhydrous and isomorphous, as Mitscherlich 

 has shown with the potassium-salt. The ammonium was estimated 

 as the double potassium-salt, and the perchloric acid as potassium- 

 salt insoluble in absolute alcohol. Analysis gave : 



NH 4 



CIO, 



(2) Ammonio-perchlorate of Copper, 2(NH 4 )0 Cu C1G 4 . 

 This salt is anhydrous, and was obtained in dark-blue crystals, 

 which on exposure to air turn green, but do not deliquesce. It is 

 best prepared by dissolving carbonate of copper in dilute perchloric 

 acid, and adding an excess of ammonia. The crystals are readily 

 obtained by pouring a layer of strong alcohol on to the surface of the 



* Roscoe, Chem. Soc. Quart. Journ. vol. xiii. p. 14G. 



