RESEARCH FOR ARSENIC AND ANTIMONY. 
679 
in which pyrites or ochreous compounds are found, I examined 
the dry residue of a gallon of Thames water by the distillation 
process, and found therein, besides sulphur, a trace of a sub¬ 
stance resembling metallic arsenic. It would require, pro¬ 
bably, the residue of several gallons to determine the question 
distinctly. 
7. Mud or sediment from the Thames. —Some of this mud 
was collected at low water, on the west side of London Bridge. 
It was taken partly from the surface, and from a few inches 
in depth. Two ounces of the mud in a dry state, the water 
(forming 34 per cent.) having been expelled in a water-bath, 
were distilled with two ounces of pure hydrochloric acid. 
One ounce of a clear and colourless acid liquid was obtained 
in the receiver. It was placed in the tube-apparatus with zinc, 
and the gas being previously dried, and deprived of any 
sulphur, was passed into a solution of nitrate of silver. After 
a short time there was a dark metallic deposit of the usual 
black precipitate, indicative of the presence of arsenic ; and on 
applying heat to the current, a deposit of metallic arsenic was 
procured, which was estimated at not less than the l-2000th 
of a grain. I am informed that, during the last summer, no 
chemical liquids have been introduced into the river for the 
purpose of deodorizing it; hence, the presence of arsenic in 
the mud cannot be ascribed to the poisoning of the water by 
the use of arsenical chloride of iron. The arsenic must be 
derived either from factories on the banks of the river, or 
from the arsenic naturally diffused through soils containing 
oxide of iron. 
In these instances, it may be remarked, the arsenic was in 
an insoluble form.* 
[To be continued .) 
* It is now well-known that a large number of mineral waters in France 
and Germany contain arsenic. In the ‘ Annuaire de Chimie’ for 1849, p. 
2 77, there is a list of forty mineral waters, including six of the well-known 
Vichy waters, which contain arsenic. Those of the Upper and Lower Rhine 
also contain this substance. (See ‘Annuaire/ 1848, pp. 189 to 194.) The 
waters of the Baths of Alexis, on the Hartz, evidently derived the arsenic 
from arsenical pyrites in the soil. According to Dr. Hoffmann, the Wies¬ 
baden water, which is generally considered a wholesome water, contains one 
grain of white arsenic in a hundred and sixty-six gallons. (‘ Chemical 
News/ August 11th, 1860, p. 101.) This is a larger proportion than that 
found in the water supplied to a country town above referred to (p. 53). 
The mud or ochreous sediment of these waters also contains it. (‘Annuaire 
de Chimie/ 1848, pp. 189—194.) It is probable if the sediment of most 
of our rivers was examined, arsenic would be frequently found therein as a 
natural constituent. This method of analysis will be found convenient for 
detecting arsenic in waters. An acid salt of iron is always produced during 
the distillation, but, with ordinary care, this does not pass over with chloride 
of arsenic so as to affect the subsequent steps of the process. 
