PRESENCE OF ARSENIC. 593 
analyst, of a mere trace of the poison sought for. 
From these remarks it will be in some degree 
apparent how much before the year 1836 we were 
wanting, in regard to our known means of testing 
for arsenic, a method by which we could not fail in 
detecting and exhibiting it, when present in very 
minute quantity, in such complex organic materials 
as we might have to make the subject of investi- 
gation. 
In the year mentioned, Mr. James Marsh, of 
the Royal Arsenal, Woolwich, published a mode 
of operating which appeared in a great degree 
to supply what was wanting: and, in viewing his 
discovery, whether we look upon the principle 
upon which it is based, or upon the apparatus 
which he used in carrying it into effect, we cannot 
but admire its beauty; both the principle and 
the apparatus being such as for simplicity will 
not readily be superseded, and the principle one 
which forbids its actions to be frustrated by the 
impediments offered by organic substances.* 
* The large gold medal of the Society of Arts of London 
was awarded to Mr. Marsh, for his discovery. His communi- 
cation is printed in the 51st volume of the Transactions of 
the Society of Arts, and in the 21st volume of Jameson’s 
Edinburgh New Philosophical Journal. 
4F 
