The solution of oxalic acid is made by dissolving 2.25 grams of
re-crystallised oxalic acid (H_{2}C_{2}O_{4}.2H_{2}O) in water and
diluting to 1 litre. One c.c. = 0.001 gram of lime (CaO), or 0.0007857
gram of carbon dioxide.
Take 100 c.c. of the same lime-water, to which add the same amount of
phenolphthalein as before. Titrate. The difference between the two
readings gives the amount of "acid" equivalent to the lime-water
neutralised by the carbon dioxide. The number of c.c. thus used up, when
multiplied by 0.3989, gives the number of c.c. of carbon dioxide (at
0° C. and 760 mm.) in the volume of air taken. This volume, which is that
of the bottle less 100 c.c., must in accurate work be reduced to the
normal temperature and pressure.[122] The percentage by volume can then
be calculated.
PRACTICAL EXERCISES.
1. In a gasometric determination 71.3 c.c. of gas were obtained from
0.2055 gram of mineral. The "volume corrector" reading was 102.2 c.c.
0.3445 gram of pure carbonate of lime gave 74.1 c.c. The "volume
corrector" reading was 100.6. What is the percentage of carbon dioxide
in the substance?
2. What volume of dry gas at 0° C. and 760 m.m. pressure should be
obtained from 0.3445 gram of carbonate of lime? 1 c.c. of CO_{2} under
these conditions weighs 1.97 milligrams.
3. A sample of coal is reported on as follows:--
Specific gravity 1.
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