178 F. H. Storer—Schenbein’s Test for Nitrates, 
reaction is far too strong to admit of its being neglected, sub- 
tracted, or allowed for, when searching for traces of bith 
Hence it happens, that in highly dilute solutions of ieee 0 
potash it is impossible to detect the nitrate by means of i - 
starch as ordinarily applied, not because the products of the 
reduction of the nitrate by zine, or the like, cease to act ee 
the iodo-starch, but because the reaction produced by t i. 
products is identical with that of the peroxide of h yin tha 
is formed simultaneously with them, and which woul 
formed just as well in pure water totally devoid of nitrates. ; 
Whenever the degree of coloration of the iodo-starch obtained 
in testing for a nitrate according to Schcenbein’s mies 
less intense than the tint obtainable from 0-0001 gram Fi oe 
(=0:000187 gram KNO,) in 50 cc. water it is difficult to sige 
whether the coloration may not be wholly due to peroxt i de 
hydrogen. It is easy, at all events, to obtain as much eae 
of hydrogen by boiling cadmium, zine or amalgama ad ee? 
with mere water, as will give a reaction with ree 5 o 
zine-starch equal to that obtainable from 0:00005 gram Mi 
perhaps even more. The following experiments will illus 
this point. : 
A. To 50 ¢.c. of pure water 000005 gram N,O, (in the = 
of 0:0000936 gram of nitrate of potash) was added, the mx 1 
ask, then cooled, transferred to a porcelain capsule, acidulated 
and tested with iodo-zine starch. : ter to 
€ same experiment was repeated with pure wa 
which no nitrate had been added. : ad instead 
me as A., with the exception that zinc was used ins 
of cadmium. : 
. Same as B., with the exception that zinc was used instead 
of cadmium. darkened 
The four capsules were placed side by side under a a ap- 
bell glass and left to stand over night. On examinatioe ad 
peared that while the contents of capsules B, C and Ds f cap 
to be of one and the same depth of color, the contents re pe? 
sule A were distinctly lighter colored than those of eit and 
the other dishes.) These ex riments were srmultaneer ule 
care was taken that they should be strictly compa ee 
one with another. Each experiment was conducted at ie 
nitrate were being tested for. Equal surfaces of me ids, in 
nearly as might be, were exposed to the action of the liquias 
each instance. 
