The Students' Guide in Quantitative Analysis - Free Ebooks Library

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APPENDIX.
the whole Uibe is red hot and the evolution of Ihe gas
f hen he v,t
^^^^^ ^ .^^^ ^^ ^^^^^^^ ^^^^^^^^ ^^^^
[^rl^^^S^'-toU.
o.her U.b or the U tube......
r h^nd of the tube, n.d dr.w . -rrent o a. .oug or a fe.
• ... Dptich the U tube and wash the contents into a Ueaker
:;;':::da°t:l add a few drops or the cochineal solution, and
titrate.
DETERMINATION I5Y THE SODA-LlMF. METHOD.
Select a tube of hard glass 14 to 16 inches long, draw one end of it
to a fine point, and to the other end fit a cork, throu-h which is passed
a tube bent at right angles, the other end of wlilch passes through a
cork closing lightly one arm of a 6-inch three-bulbed U tube with
srhss stop-c'ock, Into the combustion tube first slip a loosely fitting
plug of asbestos previously ignited, and then U to 2 inches of sodalime.
Weigh out from 0.7 to 2.8 grams of the substance to be
analyiied, and mix it on a piece of glazed paper or porcelain mor-
tar with some finely pulverized soda-lime, and introduce the mix-
ture into the combustion tube. The paper or mortar is tiien rinsed
out with a small quantity of soda-lime and poured into the tube.
The tube is then filled up to within i to 2 inches oi the open end
with granulated soda-lime, then with a plug of ignited asbestos.
A free passage is formed for the evolved gases by holding the
tube in a horizontal position and tapjjing gently on the table. In-
troduce the prepared combustion tube into the furnace, letting the
open end project a little so as not to burn the cork, supporting
the U tube by a clamp. The tube is then gradually heated, commencing
at the fore part, nearest the cork, and progressing slowly
towards the tail. The combustion should be conducted so as to
obtain a steady and uninterrupted flow of gas. When properly
carried out, the acid in the U tube is never colored. When the
acid begins to recede attach the aspirator to the other limb of
the U tube, and start it slowly, then break off the point of the
combustion tube and draw a current of air through the apparatus
for a few minutes, in order to sweep all the .ammonia into the acid.
Detach the U tube and wash the contents into a beaker or
ponx-tain basin, add a few drops of an alcoholic solution of cochi-
neal, and titrate.
The standard acid and alkali to be the same as that used in
the Ruffle method.