ee, - 
On Tests oi the Discovery of Arsenic. 155 
a XIV.— On ren for the discovery of Con in a let- 
ter, addressed to the Editor: by Tuomas Coorer,M. D- 
Professor of Chemistry, and acting President in ‘the Col- 
. rege of South Carolina ; to which are subjoined, explana- 
- tory observations, by Dr. T. D. Porter, @ tutor in the 
_same Institution. 
REMARKS. 
Dr. Porter’s dissertation, from aivehi some experiments 
are cited, Vol. IIT. 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 rer actually published, the Editor, although 
at the time in South-Caro arolina, did not hesi- 
tate to quote ohne 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 See eee: 
- Colunbia, South Carolina, Aug. #3, 1821. 
Dice Sia : | 
~ Tobserve in the May number of your Journ P- 354, a 
sugary of experiments on the Tests for Arseni y Dr. 
TeD: Porter, one of the tutors of the Sout Careting' 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 aid of arsenic ; of which therefore, that green col 
is no exclusive indication. 2dly, That in the production of 
‘Scheele’s green, by sulphat of copper carbonat of potash and 
wg 3—chromat of potash may be substituted for the arse- 
nic ; producing a precipitate not to be distinguished by the 
pie from Scheele’s green. 3dly, That the yellow precipi- 
ate produced in a solution of arsenite of potash, or arsenious 
