ON THE IMPURITIES OF COMMERCIAL ZINC. 8l 
Š 
Philadelphia, was purer than the commercial acid with reference to arsenic as well as to 
lead; indeed, in one experiment it yielded no sensible deposit in the reduction-tube, but 
in several subsequent experiments with pure zinc, in which we attempted to use Rosen- 
garten's acid instead of that purified by ourselves, we obtained faint deposits which pre- 
cluded its use, and showed it to be untrustworthy in such delicate examinations for arsenic 
by Marsh's process. To the “chemically pure" sulphuric acid made by Powers and 
Weightman of Philadelphia, precisely the same remarks apply ; it is unfit for use in any 
research where scrupulous accuracy is necessary, and of which the results are worse than 
worthless if they be not certain and impregnable. It may be granted that the amount 
of arsenic in any small quantity of these acids is really too minute to be of any conse- 
quence, except in the most refined experiments. On the other hand, it must be remem- 
bered that in some pharmaceutical processes, and in many chemico-legal examinations for 
arsenic, in which a large amount of acid is often necessarily used, the whole of the arsenic 
contained in the reagents employed is, by the very nature of the process, concentrated and 
condensed into a very small compass. For example, in a poisoning case in which the chem- 
ist is obliged to destroy by acids any considerable portion of the body, as is often the case, 
it may be necessary to use many pounds of sulphuric or chlorhydric acid, and the very 
care and pains with which the chemist labors to concentrate every grain of arsenic in 
that organic matter into the small glass of liquid, which he finally tests by Marsh's 
; process, also concentrates into the same glass all the arsenic contained in all the reagents 
which he has employed in the whole process. Under such circumstances the existence 
of any arsenic in sulphuric acid, capable of exhibition from a few cubic centimetres of 
the acid, becomes a fact of the utmost moment. From neglecting this arsenic in sul- 
phuric acid arose the long controversy concerning normal arsenic in the animal body. 
To the objection that Marsh's test is too delicate, and that we should find all the ele- 
ments everywhere if we had for each of them a test as refined as Marsh's for eme it 
may be replied, first, that Marsh's process is not thought too delicate to base vital con- 
clusions upon in difficult examinations for arsenic in poisoning cases, and secondly, 
that facts are not to be met by a theoretical objection, which is at any rate purely 
speculative, and furthermore is no objection if, as is certainly possible, the theory be 
true. 
We are aware of the common opinion, that sulphuric acid made from Sicily sulphur 
contains no arsenic,* and we do not propose to explain the source of the arsenic found 
* For a strong statement of this opinion, see Ure's Dictionary of Arts, Ae, 4th edition, Boston, 1853, 
Vol. Il. pp. 791, 799. 
VOL, VIII. 11 
