354 Tests for Arsenic. 
in pencil—* From the number of impressions taken from 4 
similar plate to this, we have no doubt of a two 
hundred thqusand proof impressions from this plate 
When it as recollected that the common number of proof 
oo is two thousand, and that one plate —s 
affords more than four or five thousand prints, Mr. Perkin 
invention may well be regarded as one of great value, aid 
as enhancing, in a high degree, the importance of the pro- 
deouane of the pencil and the graver, so that statuary has 
any superiority in this respect, while it has no 
we of multiplying copies, except the slow and tedious 
ones by which the originals are produced, or the substitu- 
tion of plaster casts. 
Arr, XVILI.— Tests a Tor Arsenic.—Eprtor. 
Jie is pa Pa rea 4 
obater: theta is1 is any test sy arsenic, gear can be a eee 
relied on, to such an extent as to justify, on that ground 
alone, the condemnation of an accused person. Some ex- 
perience, in such cases, has produced in us an increasing 
impression, that nothing short of the actual production of 
the metallic arsenic can be safely relied on for the above - 
purpose, although various tests may serve, more or less per- 
fectly, to guide the inquiries, and to influence the opinion 
of the Soe chemist. 
, Dr. T. D. Porter, now a member of the faculty 
of the t niversity of South Carolina, in his inaugural disser- 
tion states, that he finds, on repeating some of the popular 
afiertnctie with onion juice, which were some time since 
published in the newspapers ;—that the onion juice, with 
the solution of sulphate of copper, (blue vitriol,) but without 
the carbonate of potash, produces, in a weak arsenical solu- 
tion, “a shade like Scheele’s s green;” but, if carbonate of 
in 
