186 F. H. Storer—Scheenbein’s Test for Nitrates. 
water were boiled upon cadmium for five minutes; 50. ¢. of 
the water were then poured off to be tested, while two drops of 
dilute sulphuric acid were added to the flask, and the acidu- 
lated liquid was again boiled for five minutes with the cadmium. 
On decanting and testing the acidulated liquid with iodo-starch, 
it gave no coloration, not even after the mixture had stood over 
night, while on testing the portion that had been boiled with- 
out acid it gave a strong coloration in due course. 
To see if hydrogen alone would so quickly destroy the 
peroxide, a stream of hydrogen gas was made to flow during 
five minutes through a solution of peroxide of hydrogen, pre- 
pared as above, that was kept at the temperature of boiling. 
But the liquid thus treated gave almost as strong a reaction 
with iodo-starch after the passage of the hydrogen as it had 
done before. 
On trying whether some one of the more common metals 
might not perhaps be used in testing for nitrates by the new 
method, it appeared that neither of them is on the whole so 
well fitted for the purpose as cadmium. Thus on repeating the 
foregoing experiments, with zinc, amalgamated zinc, aluminum, 
and iron, it appeared that while no peroxide of hydrogen was 
formed on boiling acidulated water upon these metals, neither 
of them was so well fitted as cadmium to reduce nitrates to 
nitrites in acidulated solutions. From zine and from amalga- 
a considerably stronger solution a reaction was obtained. ‘led 
solution containing 0°01 germ. N,O, in 100 cc. water bo 
0-01 grm. N,O, in 100 cc. water after adding to ita sma” 
os of acidulated sulphate of silver and boiling the ™ 
n n 
re ~ iron. Payee t 
Both lead and magnesium easily reduce nitrates to nitrites” 
¥ 
