7 
182 F. H. Storer—Schenbein’s Test for Nitrates. 
has remarked, it seems to be immaterial whether the nitrate 
solution be boiled for a few moments with the cadmium or zine, 
or left to stand for some hours in the cold in contact with one 
solution.t The capsule, with its contents, was then placed 
under a darkened bell-glass and examined at stated intervals 
_ Tested in this way, a solution of nitrate of potash, containing 
* The dilute sulphuric acid is prepared by mixing one volume of oil of vitriol 
ater, boiling the mixture for an hour, and finally 
adding enough pure water to that which has e pated. : 
+ The solution of iodo-zinc-starch is prepared as follows, after Kubel-Tiemant, 
“ Anleitung zur Untersuchung von Wasser,” Braunschweig, 1874, p. 140: Rub 4 
mortar wi 
a 
: h in a porcelain ith a li ial 
milky liquid, little by little, into a boiling solution of 20 grams pure commerci 
* E . . . fay e mixture 
is dissolved in rain-water to color the liquid strongly ; the : 
for 24 hours, and then transferred to a copper still. A lump of lime is added 
re is distilled slowly, the first fractions of distillate being re} 
nitrites with iodo-zinc-starch, plus acid, it will not show any trace of colorati 
Ae : 
the end of an hour, and will seldom show any appreciable tinge of colo 
eft to stand over night, on ding for 24 hours shade 
of color will usually appear. I have commonly ted dency to giv? 
reaction to the presence o: i S trace of nitrite, but it is not 1m 
i mal eans 
that it may be due to peroxide of hydrogen that has been formed by m' 
thi - It would undoubtedly be better, when ee to 
; ch Wa 
. 
pared, by acidulating with acid sulphate of soda the pure water obtained = partis 
Is) and istilling i in a glass k. Free nitrous ac ie 
; at first 
as well as from peroxide of ydrogen. Sx te 
Most well waters it should be said, are, if anything, rather better than rain-¥® 
ter for preparing a pure product. .- instead 
By making the mixture of permanganate and water alkaline with lime 
Bn ‘ahatgnberrat- diag ich contaminate #? 
tie ane avcldnd. compounds which almost always 
