an Impurity of Metallic Zine. 393 
phurie acid which gives no arsenic in Marsh’s apparatus.” With proper 
understanding with what is here meant by “ Marsh’s apparatus,” this 
statement is as true now as it was twenty years ago. The committee 
relied chiefly upon the production of arsenical spots on porcelain, and 
‘ough they recommended a form of apparatus adapted for heating the 
applied by the committee of the French Academy; Otto’s apparatus is 
More sensitive than that used by this committee, and will detect the pre- 
sence of arsenic in quantities too small to produce sensible spots. It is 
self-evident that the continuous deposition of arsenic from astream of hy- 
gen as it flows steadily through a very fine tube for an hour or more, 
Would exhibit an amount of arsenic too minute to give the slightest per- 
ceptible spot in the instant during which the porcelain surface is held in 
the burning jet of gas, The first reaction is prolonged and accumulative, 
the second is intermittent and instantaneous. Blancard,* in commentin 
Upon the statement regarding the ease of obtaining pure zinc, which is 
sometimes antimony, sometim times both. 
The same explanation should accompany the statements of Orfila, with 
Sent in zine and acids becomes a matter of a very serious concern. 
p pqpingler’s Polyt, Jour., 1841, lxxxii, 425, from Jour. de Pharmacie, Sept., 1841, 
t Annales d’Hygidne Publique, 1839, xxii, 404. + Ibid, 411. § Ibid, 404. 
Ax. Jour. Sci.—Szconp Series, Vor. XXXII, No. 96—Nov., 1861. 
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