Proceedings of the British Association, 567 



of this important acid. It is well known, that, in the making of 

 sulphuric acid, when the acid in the chamber reaches the specific 

 gravity of 1.450, it is impossible to go beyond this point without in- 

 creasing the proportion of nitre ; and even with an increased proportion 

 of nitre, the product of acid is less than it ought to be. The reason is, 

 that sulphuric acid, of the specific gravity of 1.450, acts very slowly 

 in decomposing the white compound; and acid of the specific gravity of 

 1.500 will not act upon it at all, but, on the contrary, it has a tendency 

 to dissolve and retain it. — Mr. Blyth demonstrated these facts by 

 experiments. — M. Adolph Rose states, that when sulphuric acid, con- 

 taining the compound, is concentrated by distillation, at one part of 

 the process pure acid comes over; and when the acid in the retort 

 has reached the specific gravity of 1.84, it will be found, if examined, to 

 contain nitric oxide. It follows from this, that, when sulphuric acid is 

 raised in the chamber above the specific gravity of 1.500, it will be 

 found, after being rectified, more or less contaminated with the nitrous 

 compound. He made a number of trials, to ascertain the effect of 

 the nitrous compound upon indigo. Some of the compound was dis- 

 solved, by the aid of heat, in sulphuric acid of specific gravity 1.600. 

 To this solution he added some drops of a strong solution of indigo 

 in pure rectified sulphuric acid. The blue colour of the indigo was 

 immediately destroyed. M. Adolph Rose also states, that, if rectified 

 sulphuric acid, which is contaminated either with nitric acid or nitric 

 oxide, be diluted with twice its bulk of water, and concentrated by dis- 

 tillation till it reaches the specific gravity of 1.84, the concentrated acid 

 will be found to have been freed from both of these compounds. It 

 follows, from this experiment, that, in order to obtain sulphuric acid 

 sufficiently pure to be used in the preparation of sulphate of indigo, 

 it would only be necessary to draw the acid from the chamber at a low 

 specific gravity, not higher perhaps than 1.300 or 1.350. Rectified 

 sulphuric acid, prepared from acid drawn from the chambers at the 

 above strength, if found to be perfectly free from all nitrogeneous com- 

 pounds, will be a great acquisition to the woollen dyer in the prepara- 

 tion of his sulphate of indigo ; and when we consider the large quanti- 

 ties of acid used for this purpose, it will be admitted to be a subject 

 of great importance. 



Section C— GEOLOGY AND PHYSICAL GEOGRAPHY. 



1. ' On the Physical Structure of the Appalachian Chain, as exempli- 

 fying the laws which have regulated the elevation of great Mountain 

 Chains generally,' by Professors H. D. Rogers and W. B. Rogers. 



