On Tests for the Discovery of Arsenic. 155 
Art. XIV.— On tesis for the discovery of Arsenic, in a let- 
ter, addressed to the Editor: by 'Tuomas Cooper, M. D. 
Professor of Chemistry, and acting President in the Col- 
lege of South Carolina ; to which are subjoined, explana- 
tory observations, by Dr. 'T. D. Porter, a tutor in the 
same Institution. 
REMARKS. 
Dr. Porter’s dissertation, from which some experiments 
are cited, Vol. III. pa. 354 of this Journal, was evidently not 
intended for publication; but, as inaugural dissertations of 
medical graduates are held liable to publication, and are 
in most Institutions actually published, the Editor, although 
Dr. Porter was at the time in South-Carolina, did not hesi- 
tate to quote some facts, which appeared to him worthy of 
notice. He does not regret the step, especially as it has been 
the means of drawing from Dr. Cooper the following valua- 
ble letter. Dr. Porter happening to be here (New-Haven) 
at the time of its reception, it was thought no more than 
- fair to shew him the letter, and to receive his reply, which 
is annexed.—Editor. 
Columbia, South-Carolina, Aug. 13, 1821. 
Dear Sir, | 
I observe in the May number of your Journal, p. 354, a 
summary of experiments on the Tests for Arsenic, by Dr. 
T. D. Porter, one of the tutors of the South-Carolina Col- 
lege here. They are intended to shew, Ist, that the green 
colour produced by the union of arsenious or arsenic acid 
and copper, may be produced from copper, by onion juice, 
by coffee, and more especially by chromat of potash, with- 
out the aidof arsenic; of which therefore, that green colour 
is no exclusive indication. 2dly, That in the production of 
Scheele’s green, by sulphat of copper carbonat of potash and 
arsenic ;—chromat of potash may be substituted for the arse- 
nic; producing a precipitate not to be distinguished by the 
eye from Scheele’s green. 3dly, That the yellow precipi- 
tate produced in a solution of arsenite of potash, or arsenious | 
