214 Useof Hydrogen Gas in analyzing Minerals Waters. 
vessel containing the snl phureous water through which it bubbles 
in a brisk but not violent stream. he gas, more or less charged 
with sulphuretted hydrogen, is led into a third vessel containing 
either a solution of nitrate of silver to which ammonia has been 
added, or an alkaline solution of arsenious acid, to arrest the sul- 
phnretted hydrogen. The former solution is greatly to be pre- 
ferred where the mineral water is only feebly sulphureous. The 
sulphur thns precipitated is to be determined in the nsnal way. 
Suppose the mineral water to contain free hydrosu!phuric acid 
together with sulphids say of potassium and magnesiuin, we may 
proceed as follows: 
1, We determine for a given volume of the water the total 
amount of sulphur present by the use of chlorid of copper or ni- 
trate of silver. , 
amount of free hydrosulphuric acid in the water. 
- We apply heat to the flask containing the sniphureous wa- 
ter which has been thus treated, so as to cause gentle boiling, a 
the same time supplying the upper space with hydrogen in@ 
moderate but steady stream. It will be found that below t 
point of ebullition the issuing hydrogen will give scarcely a trace 
of hydrosulphuric acid, but as soon as the liquid begins to boil, 
the stream of vapor and hydrogen plainly shows the presence of 
this substance, then slowly evolved by the decomposition of the 
sulphid of magnesium or calcium. ; 
. We treat the remaining lignid with chlorid of copper, the 
arseiiious solution, to determine the sulphur of the alkaline stil- 
phid which is the only sulphur compound left in the water. 
‘The sum of this and the sulphur of the free hydrosulphurie a¢ 
subtracted from the total quantity of sulphur gives that of the 
sulphid of magnesium. 
e find that a proportion of hydrosulphurie acid too small 1 
be quantitatively determined by precipitation’ from the wale! 
itself can be ascertained by the use of the stream of hy aya 
It is only necessary to pass the gas which has been trausmitte 
through the water into an ammoniacal solution of nitrate of 
ver in a long test tube or Liebig’s bulb. By continuing the ac 
tion for one or two hours we obtain a precipitate capable of | ” 
separated. ae 
When the water contains no sulphid of magnesium oF of 
cium, it is merely necessary, after determining the total amount 
sulphur present, to boil the liquid in an atmosphere of hydrog®” 
