124 Iodine a Reagent for Hydrosulphuric Acid. 



tincture of iodine, (it not being among those ordinarily used ;) I 

 found that the decomposition of the hydrosulphuric acid by this 

 metalloid, was complete and instantaneous, and that one could 

 determine, in a very easy manner, the precise point at which the 

 decomposition of the hydrosulphuric acid is achieved, or when 

 the iodine no longer enters into combination. I conclude, from 

 this fact, that, with a tincture of which I know before hand the 

 proportions, I shall be able to ascertain, by the quantity of iodine 

 employed to saturate a litre of the sulphurous water, the precise 

 amount of hydrosulphuric acid which it contains. 



"Moreover, I am able to ascertain the quantity of iodine em- 

 ployed, without the use of a balance, by the means of an instru- 

 ment which I call a sulphohydrometer. This instrument is a 

 graduated tube, which allows the tincture of iodine to flow from 

 an elongated extremity with a capillary opening, the other ex- 

 tremity being closed by a stopper. 



" To employ the sulphohydrometer, we take a certain quantity 

 of the sulphurous water which we may wish to analyze, and 

 placing it in a porcelain capsule, add a few drops of a very clear 

 solution of starch, and then allow the tincture of iodine to fall 

 upon it, drop by drop, from the instrument, previously filled to 

 the point marked 0°, and continue the addition so long as no 

 change takes place in the color of the water, favoring the reac- 

 tion by agitation with a glass rod. So long as there remains the 

 smallest trace of hydrosulphuric acid, the iodine disappears as 

 fast as it is introduced, and the starch, upon which iodine in a 

 state of combination does not act, gives rise to no coloration of 

 the liquid until the hydrosulphuric acid is completely saturated, 

 when the minutest addition of iodine at once strikes a blue color 

 with it. We then examine how many degrees of tincture have 

 been employed, and knowing the strength of it, we are enabled 

 to calculate the quantity of hydrosulphuric acid decomposed by it. 



"This method of analysis, independent of its aflbrding results 

 of the most accurate character, has the additional advantage of 

 being executed in so short a space of time, that one may make 

 from fifteen to twenty experiments in less than one hour, and at 

 the same time be perfectly sure of committing no error. It is 

 also so easily put into practice, that any physician or intelligent 

 person may apply it, and assure themselves daily of the variation 

 in the strength of the sulphurous waters caused either by atmos- 

 pheric changes or an admixture with rain water. 



