an Impurity of Metallic Zine. 389 
Vieille Montagne zinc; 200 grammes of it with pure acid yielded a 
deposit in the reduction-tube, fatal io its use in any delicate experiments. 
Manufactured from silicate of zinc, and we therefore expected to find this 
papi purer than the ordinary English zine made from blende; but, on 
e 
at he has examined many specimens of English and foreign zines, and 
could never obtain any indications of arsenic when the sulphuric acid 
Was pure. The explanation of this discrepancy is to be found in the fact, 
that the test applied by Brett, although essentially Marsh’s test, had not 
extraordinary delicacy which is insured by Otto’s form of Marsh’s 
4Pparatus, 
* Philosophical Magazine, 1842, [3], xx, 404, 
