ARSENIC IN ARTIFICIAL MANURES. 
661 
a very perceptible white sublimate was produced, which, on 
being dissolved in hot distilled water, and this solution added 
to a Marsh’s apparatus in operation (the hydrogen flame, 
which before the addition of the solution did not give the 
slightest indication of a metallic stain on a cool piece of white 
porcelain being placed over it), produced immediately the 
characteristic stains of metallic arsenic in a most striking 
manner, proving beyond all doubt that the matter deposited 
on the copper was metallic arsenic, and the sublimate arseni- 
ous acid, formed during the heating of the inetal. 
This experiment was repeated with the same results, using- 
21 lbs. weight of turnip taken from another of the turnips, it 
being previously peeled. I may observe that in these, as 
well as in the foregoing experiments, I was most careful that 
no source of fallacy might arise from the arsenic being derived 
from the reagents employed, which were previously ascer¬ 
tained to be free from arsenic; and to avoid all possibility of 
error, comparative experiments with the reagents alone were 
made in almost every step of the different investigations. 
The turnips I experimented on were grown by Mr. John 
Rathbone, Dunsinea, Co. Dublin, and I was informed that 
six hundred-weight of superphosphate had been used to the 
Irish acre, the superphosphate being previously mixed with 
peat and clay, in the proportion of one part of superphosphate 
to three parts of the mixture of peat and clay. 
These experiments appear to me to be perfectly conclusive 
as to the power possessed, by some plants at least, of taking 
up arsenic when it is introduced into the soil by artificial 
manures which contain it, even when they are employed in 
the usual way and proportion by agriculturists, and how 
objectionable it is to use any materials in the preparation of 
those manures which will introduce so destructive and dan¬ 
gerous a substance as arsenic into the soil. 
I thought it would be desirable to ascertain the proportion 
of arsenic present in the brown sulphuric acid used by one 
of our Dublin manufacturers for the purpose of making 
superphosphate and other manures. In 12 fluid ounces of 
the acid, by the usual methods of ascertaining the quantity 
of arsenic in such cases, 1 obtained an amount of metallic 
arsenic equivalent to about 12 grains of arsenious acid, or 1 
grain to each fluid ounce ; and the ounce of acid weighing 
about 800 grains, the arsenious acid would be 1-800th part 
of the weight of the acid, which would be equivalent to about 
2*8 lbs., or nearly 3 lbs. weight in the ton of sulphuric acid. 
But it is probable that the generality of brown sulphuric 
acid employed contains much more arsenic than this sample 
xxxii. 87 
