The
volume of the gas is then read off. In adjusting the level, account must
be taken of the sulphuric acid in the measuring-tube; this is allowed
for by having the mercury higher in the other tube by, say, 1 mm. for
each 6.5 mm. of sulphuric acid, or it is counterpoised by an equal
height of sulphuric acid in the levelling-tube, in which case the two
mercury-levels are made to correspond. On opening the tap after reading
off the volume, there should be no change in the level of the mercury.
If it should rise or fall a little, a slight increase or decrease (say
0.1 c.c.) is made to the volume previously read off.
In working with nitrate of soda, &c., in the bulb nitrometer, it is
necessary to take a quantity of the substance which will yield more than
100 and less than 150 c.c. of the gas.
FOOTNOTES:
[103] Na_{3}AsO_{3} + H_{2}O + 2I = Na_{3}AsO_{4} + 2HI. The acid is at
once neutralised.
[104] Mr. Thomas Gibb is the originator of this ingenious process.
[105] By taking hold of the water present, it may prevent the
dissociation of arsenious chloride.
[106] It is difficult to get ferric chloride free from arsenic; but the
following treatment will remove 80 or 90 per cent. of the arsenic
contained in the commercial material:--Dissolve 2 or 3 lbs. of ferric
chloride with the smallest amount of water that will effect solution
with the addition of 100 c.
Pages:
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741