1822.] Mr. Smithson on Arsenic and Mercury. 127 
alkalinity and acidity, and that this something is of an impon- 
derable character, and dependent on galvanism. 
«In the number of your journal for October last, I gave my 
reasons for believing in the existence of material imponderable 
principles producing the phenomena of heat, light, and electri- 
city. The co-existence of these principles in the medium 
around us, their simultaneous or alternate agency and appear- 
‘ance during many of the most important processes of nature, 
‘seem to me to sanction a conjecture, that as ingredients in pon- 
derable substances they may cause those surprisingly active and 
wonderfully diversified properties usually ascribed to apparently 
inadequate changes in the proportions of ponderable elements. 
“< In obedience to your request, I have thus displayed the ideas 
at present awakened in my mind by these obscure and interest- 
ing phenomena. I am not willing to assume any responsibility 
for the correctness of my conjectures. Possibly they may excite 
in you further and more correct speculations.” 
ARTICLE V. 
On the Detection of very minute Quantities of Arsenic and 
Mercury. By James Smithson, Esq. FRS. 
(To the Editor of the Annals of Philosophy.) 
SIR, 
To be able to discover exceedingly small quantities of arsenic 
and mercury must, on many occasions, prove conducive to the 
purposes of the chemist and the mineralogist, more especially 
now that a very diminished scale of experiment, highly to the 
advantage of these sciences, is becoming daily more generally 
adopted. 
But the occasion above all others in which the power of doing 
this is important, are those of poisonings. In these it is often 
of the first moment to be able to pronounce with certainty, from 
portions of matter of extreme minuteness, on the existence and 
the nature of the poison. 
Of Arsenic. 
I have already communicated the method here proposed for 
the discovery of arsenic by employing it in the analysis of the 
compound sulphuret of lead and arsenic from Upper Valais, 
pened in the Annals of Philosophy for August, 1819, but not 
aving mentioned the generality of its application, or the great 
accuracy of it, it seems not superfluous, from the importance of 
the subject, to resume it. 
If arsenic, or any ofits compounds, is fused with nitrate of 
