ARSENIC IN ARTIFICIAL MANURES. 659 
third day with a saturated aqueous solution of arsenious acid; 
and this treatment was continued for more than a week with¬ 
out its appearing to exercise any immediate injurious effects 
on the plants. At this time, however, I was obliged to leave 
home for some months, so that I was unable to continue 
longer the watering with the arsenical solution, or to observe 
further its effects on those plants. On my return I found 
that they had grown to about their full size, had flowered, 
and produced seed, showing that arsenic, though so very 
destructive a substance to animal life, had not apparently ex¬ 
ercised any decided injurious effects on those plants. 
Having collected the stalks, leaves, and pods of the peas, I 
carefully kept them for examination, to ascertain if those 
plants, under the treatment they had been subjected to, had 
taken up any arsenic. Professional business, however, of one 
kind or another prevented at the time my pursuing the sub¬ 
ject any further, and I did not resume the inquiry till recently, 
when, being engaged in the detection of arsenic in a case of 
suspected poisoning, my attention was again called to this 
subject. 
In the case I allude to, the quantity of arsenic present in 
the stomach and its contents was very minute, and I had re¬ 
course to several methods for the detection of that metal before 
I could affirm positively to the existence of arsenic; and I 
found that by employing conjointly Reinsch’s and Marsh’s 
methods, by far the most satisfactory results were obtained. 
These methods are well known. The first consists in 
boiling the suspected substance along with diluted hydro¬ 
chloric acid, together with some pieces of metallic copper, 
when, if arsenic is present, it will be deposited in the metallic 
state on the surface of the copper, giving it a peculiar steel- 
grey appearance; and on heating the copper after being 
washed and dried, the arsenic can be volatilized as arsenious 
acid, and indentified by its appropriate tests. The second 
method consists in bringing the suspected substance, in a 
state of solution, in contact with a mixture of zinc and diluted 
sulphuric acid contained in a suitable apparatus, when the 
arsenic, if present, will combine with the hydrogen being 
generated, and will form arseniuretted hydrogen, a gaseous 
compound which is characterised by its producing a stain of 
metallic arsenic when any cool surface is held over a small 
jet of the gas whilst burning. On trying by these methods 
the stalks and leaves of the pea-plants which I had watered 
with arsenious acid, 1 found that arsenic could be readily de¬ 
tected in them, and was present even in the seeds, showing 
clearly that arsenic had been freely taken up by those plants, 
