154 marsh's apparatus. 
ART. XXVII. — A MODIFICATION OF MARSH'S APPARATUS, 
For the detection of arsenic, by Mr. Morton, of the Veteri- 
nary College, being on the table, that gentleman, at the re- 
quest of the chairman, explained the difference between this 
and the instrument as usually made. Mr. Morton's appara- 
tus is similar in construction to Dobereiner's hydro-platinum 
apparatus for obtaining instantaneous light, consisting of an 
external cylindrical glass jar open at the top, and an internal 
conical receiver, in which the gas is collected and discharged 
at will through a stop-cock. Two coils of platinum wire are 
inserted in the base of the outer cylinder, the one under the 
certre of the receiver, the other external to it. The former 
being connected with the negative electrode of a galvanic bat- 
tery, and the latter with the positive, the water contained in 
the instrument is decomposed — hydrogen being collected in 
the receiver, and oxygen escaping outside. If any arsenic be 
present in the liquor, arsenuiretted hydrogen will of course be 
formed, and may be detected in the usual way. 
The advantage of this instrument consists in its obviating 
the necessity, of using sulphuric acid and zinc, which are so 
frequently found to be contaminated with arsenic. Mr. Mor- 
ton stated, that the presence of arsenic in the proportion of one 
grain to a gallon could be detected by means of this instru- 
ment. LoncL Pharm. Journ. and Trans. 
* 
