12 Prof. Daniell on Sulphuretted Hydrogen 



temperature of which varied from about 70° to 110°, and the 

 water was filled up from time to time, as it evaporated, and 

 the mixture well stirred. 



Upon examining them on the 5th of February, 1841 (three 

 months), the following was found to be the state of the jars : — 



No. 1 had a very disagreeable odour, but produced no 

 change whatever upon paper soaked in acetate of lead. 



No. 2 was perfectly sweet, and possessed, indeed, a rather 

 agreeable odour. It produced no effect, of course, upon the 

 test paper. 



No. 3 had a most insupportable sickening odour, much 

 worse than that of pure sulphuretted hydrogen, and instantly 

 blackened paper soaked in acetate of lead, throwing down 

 sulphuret of lead with a metallic lustre. 



You will have an opportunity of observing, by the speci- 

 men upon the table, that the evolution of the gas is at this 

 moment proceeding with increased energy. 



Now, the analysis of sea waters generally, and these analyses 

 in particular, show that a large proportion of sulphates is al- 

 ways present in them, and there is no doubt that extensive 

 mud-banks must be formed at the mouths of the African 

 rivers, within the tropics, consisting chiefly of vegetable de- 

 tritus, in the exact state which is most favourable to this 

 action. 



Since my report to the Admiralty upon this subject, I have 

 seen a paper in the Annates de Chimie for July 1840, by 

 Dr. Amedee Fontan, upon the Mineral Waters of Germany, 

 Belgium, Switzerland, and Savoy, in which he suggests that 

 the presence of sulphuretted hydrogen in those waters may 

 be owing to the decomposition of the sulphates which they 

 contain by vegetable matters, remarking that many of them 

 which contain little of that gas at their sources, acquire more 

 of it by their flow through the soil. There can be little 

 doubt of the correctness of this opinion. 



A curious fact has also been brought to my recollection by 

 my friend Mr. Fownes, with regard to a spontaneous change 

 which a solution of litmus undergoes when excluded from the 

 air. It becomes of a brown colour, but still it is not spoiled, 

 for the colour is restored by exposure to air. 



M. Vogel (Ed. Journ. 31, 157), who inquired into this curi- 

 ous fact, found that the solution always contains sulphate of 

 potassa, which becomes gradually decomposed with the gene- 

 ration of sulphuretted hydrogen, to the deoxidating power 

 of which the effect is owing. A few drops of sulphuretted 

 hydrogen solution produces the same effect in a few days; the 

 solution becomes brown, but speedily recovers its colour upon 



