F. H. Storer—Scheenbein’s Test for Nitrates. 179 
Repetitions of these tests gave similar or analogous results 
Sometimes the contents of one capsule in the series wou 
be more or less strongly colored than the rest and at other 
times another, but everything went to show that by this 
zine was used instead of the simple zinc or cadmium. It is 
filtered, and acidulated with sulphuric acid; but since water 
that is absolutely free from nitrates will do almost precisely the 
same thing when similarly treated, the statement is of no value 
either as regards the delicacy of the test, or the limit of its 
ap licability. 
Proof that the cause of the reaction in the water free from 
nitrates is really due to the presence of peroxide of hydrogen 
been in contact with a metal is similarly treated. —_ : 
With pure water these results are constant and invariable, 
um 
rpecated, while no such coloration was observed when sam- 
aaa rain or well water were tested in this way; far from 
oo the liquids soon acquired a rusty color, as if 
re 
Zeitschrift analyt. Chemie, 1869, i, 18 
inet, Of instead of simple ferrous sulphate, the double sulphate of protoxide of 
nmonia may be used with advantage, as was suggested by Struve, Fre- 
the text analyt. Chemie, 1869, viii, 319. Most of the tests described in 
solution of it~ made with this double salt. Two or three drops of a yy normal 
