Iodine a Reagent for Hydrosulphuric Acid. 



125 



" The conclusions that I have arrived at by my experiments, 

 are as follows : — 



" 1st. That the best known reagents for hydrosulphuric acid are 

 subject to great objections, since they do not indicate even nota- 

 ble quantities of this acid, free or combined ; a circumstance that 

 explains why its presence has not been demonstrated in waters 

 whose physical properties rank them as sulphureous. 



"2d. That an alcoholic solution of iodine, employed along 

 with starch, is a very sensible reagent for hydrosulphuric acid, 

 free or in a state of combination. It can detect, in an undoubted 

 manner, (by a comparative examination with common water,) a 

 drop of concentrated solution of any of the alkaline hydrosul- 

 phates, disseminated in one hectolitre* of water, although the 

 known reagents lose their action when the same quantity is dis- 

 seminated in only ten litres.f 



" 3d. That with the tincture of iodine and starch we can re- 

 cognize infallibly, in the weakest sulphureous waters, in those 

 where ordinary reagents are useless, not only the presence, but 

 also the quantity of hydrosulphuric acid, either free or in a state 

 of combination. 



" 4th. That the known processes for determining the proportion 

 of hydrosulphuric acid, free or combined, are so long and difficult 

 that their result is uncertain and incorrect, especially in regard 

 to waters possessing but little of the sulphureous principle." 



Table of the quantity of Hydrosulphuric Acid decomposed by 

 quantities of Iodine from ^\-^ to 10 grains. 



* Hectolitre, about 26^ gallons. 



\ Ten litres, about 2^ gallons. 



