146 Selections from Foreign Science. 



cially whilst weigjhing the acid, on washing out the sulphate formed, 

 in moderating the intensity of heat during the combination, &fc. 

 The mean of three experiments gave, for 1 of acid operated upon, 

 2.886 of sulphate of baryta, which being equivalent to .992 of dry acid, 

 gives a deficiency of 0.008, so that the acid cannot contain more 

 than this quantity of water : but, as it is difficult to make the 

 experiment exactly, and every error would involve a loss of this 

 kind, and moreover, as it is not at all a probable proportion of 

 water, there is every reason to believe that the solid substance 

 ■which may be obtained by sublimation from the fuming acid of 

 Nordhausen, is dry sulphuric acid. 



The following are the properties of this substance : it is solid or 

 liquid according to the temperature, and when liquid is more fluid 

 than common sulphuric acid; it is highly refractive; its specific 

 gravity is 1.97, at 68° Fahr. It remains fluid at 77° Fahr., but 

 below that point silky crystals form, and ultimately the whole 

 becomes solid. Once solid it is difficult to fuse, because the first 

 portions heated become vapour and propel the rest forward ; but 

 by slight pressure this is prevented. When solid it is white, 

 opaque, fuming in the air, and deliquescent. It dissolves sulphur, 

 forming brown, green, or blue compounds, according to the quan- 

 tity taken up : when water is added, the sulphur is deposited. 

 Iodine dissolved in it forms a bluish-green solution. 



Nordhausen acid is therefore essentially a mixture of common 

 and anhydrous sulphuric acid : the sulphurous acid which it con- 

 tains, though constantly produced in the process of its preparation, 

 confers no particular properties on it; and the brown colour is 

 entirely accidental. 



M. Bussy then proceeds to examine the action of heat on sul- 

 phate of iron, that being the well-known process by which the 

 fuming acid is obtained. When crystallized sulphate of iron is 

 heated, it first loses about 45 per cent, of water and becomes an- 

 hydrous ; sulphurous acid is then evolved, and ultimately very 

 dense suffocating vapours. The latter act upon mercury, and 

 therefore cannot be received over it without previous washing ; 

 but, when passed through water, and then received over mercury 

 in separate portions, it was found that though at first sulphurous 

 acid gas only came over, oxygen soon appeared, which increased 

 in proportion, until ultimately the gas was a mixture of two 

 volumes of sulphurous acid gas, and one of oxygen. The washing 

 water contained sulphuric acid, and the retort peroxide of iron 

 with a little sulphuric acid. Hence it appears, that at first 

 sulphuric acid was decomposed peroxidizing the iron, and liberat- 

 ing sulphurous acid ; that then one portion of sulphuric acid 

 rose without decomposition, and was retained by the water, whilst 

 another portion was decomposed by the heat, and produced the 

 mixture of sulphurous acid gas and oxygen. It was probable 



