230 



EDWARD DIVERS AND TAMEMASA HAGA 



We took its specific gravity, in ether, and found it to be 2.03 at 

 12°. Nothing has been published as to its melting point, except that 

 M. Schmidt placed it as neat- 200°. It has, in fact, no real melting 

 point, for, as will be shown later on in this paper, in the act of melting, 

 it completely decomposes. Its apparent melting point, as near, probably 

 as can be determined, is 205.° The observation of this point was 

 made on the driest acid, in a capillary tube, beside a Jena thermometer 

 with thread immersed, in a bath of sulphuric acid. It melts very 

 slowly at this temperature. Even at its melting point, it begins to 

 evolve vapours from its surface, but these are of its decomposition 

 products, and very slight in dry air. In fact, this volatilisation and 

 the melting point are greatly affected by the access of moist air, and 

 by any dampness in the acid used. 



Berglund described it as being quite easily soluble in water, and 

 it is so, though slowly. But it is less soluble than any of its salts, 

 except that of silver (not counting its basic mercury salt). It requires 

 o parts of water at 0°, and 2^ parts at 70°, to dissolve it. The fact, 

 that hot water is not without chemical action upon it, renders a close 

 determination of its solubility in hot water impossible. There is no 

 known solvent for it but water. 



Sulphuric acid greatly diminishes the solubility of the acid in 

 water, and readily precipitates it from its solution, and from solutions 

 of its salts. Its solubility in water is also greatly reduced by the 

 presence of sodium hydrogen sulphate. These facts largely facilitate 

 the preparation of the acid, as already described. Not more than 3 

 parts of acid per hundred of water remain in solution after concentrat- 

 ed sulphuric acid, £— £ of the volume of solution, is added, and the 

 solution left to itself for a day. A 5 per cent, solution of the acid very 

 soon deposits some of it, when mixed with sulphuric acid ; a 2^ per 

 cent, solution deposits none, even on standing, but, when previously 



