260 M. Bttssi/ on Sulphuric Acid. [Ocxi. 



must be ascribed to the unavoidable errors of experiment, and 

 the impossibility of preventing the concrete acid from attracting 

 some moisture during the coarse of it. 



The anhydrous acid liquefies at about 66° Fahr. ; it is more 

 fluid than common sulphuric acid, and has a high refractive 

 power; at the above temperature its specific gravity is 1-97. 

 To preserve it in the liquid form, it must be kept at the temper- 

 ature of 77° Fahr ; below that point silky tufts are seen to form, 

 and the liquid soon becomes quite solid ; when it has once 

 assumed that state it is difficult to remelt it, for the portions 

 which receive the first impression of the heat are volatilized and 

 lift up the incumbent mass, sometimes throwing it out of the 

 vessel to the manifest danger of the operator. It may, however, 

 be liquefied by the assistance of a slight pressure. 



Anhydrous sulphuric acid dissolves iodine, with which it forms 

 a greenish blue solution. 



Action of Heat on Sulphate of Iron, and the other Sulphates 



decomposable by Heat. 



When crystallized protosulphate of iron is exposed to the 

 action of heat in close vessels, it first loses its water of crystal- 

 lization, which amounts to about 45 per cent, and becomes a 

 white anhydrous protosulphate, composed of 28*90 of sulphuric 

 acid and 26-04 of protoxide of iron. If the heat be continued, 

 sulphurous acid is disengaged, and then very thick and suffocat- 

 ing vapours, which act on mercury if we attempt to collect them 

 over that fluid ; to prevent which it is necessary to wash the gas 

 before it is collected. 



" The apparatus which 1 use consists of a glass retort, whose 

 beak is drawn out by the lamp, and passes into a vessel filled 

 with distilled water at 122° Fahr. From this vessel proceeds a 

 bent tube, which passes under a jar, filled with and inverted 

 over mercury. 



" By gradually heating the retort to redness, at first only sul- 

 phurous acid gas comes over; after a short time it is mixed 

 with a certain quantity of oxygen, which continually increases 

 to the end of the operation. The collected gas, when examined 

 by potash, is found to consist of two parts of sulphurous acid 

 gas and one of oxygen. The water contains some sulphuric 

 acid, and peroxide of iron, sometimes still retaining a little sul- 

 phuric acid, remains in the retort." 



What passes in this operation is thus explained : — " At first a 

 portion of the sulphuric acid is decomposed into sulphurous 

 acid and oxygen, which raises the iron to the maximum of 

 oxidation; another portion is volatilized, undecomposed, and 

 dissolved by the water ; and a third portion is decomposed by 

 the heat into two volumes of sulphurous acid and one volume of 

 oxygen." 



