184 F. H. Storer—Schenbein’s Test for Nitrates. 
no better results, but rather worse on the whole. Rods of 
cadmium appeared to be somewhat preferable to those of zine, 
though not much. 
It will be observed that the results of these tests are even less 
of delicacy above mentioned. Thus, on repeating some of the 
foregoing trials and using rain-water to dissolve the nitrate, 
instead of the pure water previously used (see page 182, note) 
less favorable results were obtained. A solution of the nitrate 
equal to 0-005 grm N,O,, in 50 cc. cistern water gave no 
reaction with the iodo-zine-starch in the course of an hour. On 
repeating the trial with cistern-water that had just been boiled, 
a slight reaction was obtained, but the blue color instead of 
increasing faded away after a time and disappeared. The pro- 
portion of acid employed to acidulate the mixture is not with- 
out influence upon the delicacy of the test, and it may well be 
that in order to the best results a larger amount of acid 1s 
required than was used in the foregoing trials. The small 
quantity of the acid actually taken was chosen in order to con- 
form to Carius’s injunction that “ the addition of but little acid 
is a condition of success.” But it appeared once on peg 
the trial with the nitrate solution, in pure water, that. contain 
( ,O, in 50 cc. that while no coloration of the 
iodo-starch had appeared after some time so long as only two 
drops of sulphuric acid had been added, the reaction soon 
in on the addition of two more drops of the acid. 
The defect of the usual method of testing for nitrates having 
been made apparent, I have naturally endeavored to discover 
which should not at the same time occasion the formal 
pe of hydrogen, I have finally hit upon the es : 
utral 
solutions, as has hitherto been recommended. ntrary od 
what might have been inferred from what has been paar al 
~ eam and — what is known of the Ss ao 
water upon metals in the cold, no peroxide of DY@'o.. .. 
formed when water slightly ieidalaied with sulphuric acid 
_ boiled upon metallic cadmium; and since the reduction 
