460 
SECOND REPORT-1832. 
change is such as to reduce its saturating power one half, it would 
at once account for the silver salt containing the elements of two 
atoms of phosphoric acid, and for the fact that half an atom of 
soda is sufficient to saturate the free acid in the salt after fusion. 
Mr. Graham, who has been kind enough to make me partially 
acquainted with his results, is still occupied with the investiga¬ 
tion, and it is to be hoped that he will soon be able to clear up 
all the difficulties which the subject presents. 
In the present state of the science, the isomeric modifications 
of the compounds of phosphorus and of other elementary sub¬ 
stances, form the most interesting and perhaps also the most 
important subject of inquiry. 
Sulphur m mineral waters. —When chlorine and iodine are 
present together in a mineral water, they are both precipitated 
by nitrate of silver, and the precipitate is treated with caustic 
ammonia, which dissolves the chloride and leaves the iodide, 
which is then collected and weighed. Brandes *, however, has 
observed that the insoluble residue sometimes contains sulphu- 
ret as well as iodide of silver, and this when the quantity of sul¬ 
phur present in the water was so small as to escape detection by 
the usual tests. If the quantity of sulphuret present be large, it 
may be detected by the dark colour it imparts to the precipitated 
yellow iodide. But if small in quantity, the precipitate is to be 
fused with caustic potash, when the alkaline solution obtained 
by treating the mass with water gives with muriatic acid the 
odour of sulphuretted hydrogen, and by the further addition 
of nitric acid, vapours of iodine which stain starch paper of a 
blue colour. 
It is often a matter of some interest to ascertain in what state 
the sulphur exists in hepatic waters. In the greater part of 
such springs it has been supposed to be merely in a state of 
solution, not of combination. An examination of some of the 
German springs has shown it to be generally present, partly in 
a free and partly in a combined state, in combination w r ith soda. 
The mode of determining the relative quantities depends upon 
the employment of reagents of the two classes of metallic oxides, 
one of which is precipitated either by sulphuretted hydrogen 
or by hydrosulphurets, the other only by liydrosulphurets. 
Thus sulphate of copper will precipitate all the sulphur which 
the water contains,—sulphate of manganese only that which 
is in combination. 
Sulphuretted hydrogen , action of on nitric acid. —I have ob¬ 
served that when a current of sulphuretted hydrogen is passed 
* Selnveigger’s Neues Jahrbuch, i. p. 250. 
