148 
MR. DAVY ON A SIMPLE ELECTRO-CHEMICAL METHOD 
giving greater publicity to those facts. In the course of the present summer 
my attention has been directed to apply similar means to the detection of 
metallic poisons, a subject of acknowledged and increasing importance ; and 
the results I have obtained, and now beg leave to submit to the Society, appear 
to me both novel and interesting, and afford, if I mistake not, means more 
simple, delicate, and effectual, than any at present known for detecting the 
common metallic poisons. 
The fear of trespassing too much on the time of the Society, induces me to 
limit the present paper to one part only of the subject. At no distant period 
I promise myself the pleasure of communicating the remaining part, which 
will embrace the different electro-chemical experiments I have made on the 
other metals and their compounds, together with the application of the facts 
to the processes of gilding, silvering, tinning, &c. 
In the following pages I shall notice the simple electro-chemical apparatus, 
(or electro-chemical method as I shall call it,) employed in my experiments ; 
offer proofs of its efficacy to detect different metals, particularly metallic 
poisons ; adduce instances of the extreme delicacy and facility of the method ; 
and lastly, show, by similar evidences, that its accuracy is not impaired by the 
presence of organic substances whether vegetable or animal, or mixtures of 
both ; and that the method is therefore applicable to the detection of metallic 
poisons in all cases. I shall be under the necessity of making some minute 
(and I fear tedious) details, which I trust will be excused, as they are closely 
connected with the elucidation of the subject. 
It forms no part of my object to examine the numerous known methods of 
detecting metallic poisons. Experience, I may presume, has made me tolerably 
familiar with the details of them. The electro-chemical method here proposed 
appears to me to rival the very best of them in point of accuracy, whilst in 
facility, simplicity and delicacy, it seems superior to them all. 
2. Of the Electro-chemical Apparatus. 
The electro-chemical apparatus I used was of the simplest kind. It con- 
sisted of two different metals, generally zinc and platina, which, according to 
Sir H. Davy, form the most efficient combination ; the zinc being positive, and 
the platina negative, with regard to all the other metals. The zinc was usually 
