The solution of oxalic acid is made by dissolving 2.25 grams of re-crystallised oxalic acid (H2C2O4.2H2O) 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 CO2 under these conditions weighs 1.97 milligrams.
3. A sample of coal is reported on as follows:—
| Specific gravity | 1.315 |
| Moisture | 1.001 |
| Volatile matter | 35.484 |
| Fixed carbon | 50.172 |
| Ash | 12.028 |
| ——— | |
| 100.000 |
What is there about this requiring explanation?
4. Calculate the percentage of carbonic acid in a mineral from the following data:—
| Weight | of apparatus | and acids | 87.0888 | grams | |
| " | " | " | plus mineral | 88.8858 | " |
| " | " | " | after loss of carbonic acid | 88.1000 | " |