| v′ | = | x |
| v | 100 |
Example: Let ninety-five cubic centimeters be the volume of gas from five cubic centimeters of the pure salt (sodium nitrate), and 91.5 cubic centimeters be the volume of gas from five cubic centimeters of the sample; then
| 91.5 | = | x | , whence x = 96.31. |
| 95 | 100 |
Hence the sample analyzed contains 96.31 per cent of sodium nitrate. Since the pure sodium nitrate contains 16.47 per cent of nitrogen the sample under examination would contain
| 16.47 × 96.31 | = 15.86 per cent. |
| 100 |
It is evident that this comparative method is quite easy of application when the sample under examination has no other nitrate in it except that combined with the one base.
216. Volumetric Method of Gantter.—The process proposed by Gantter for determining the nitrogen, volumetrically, in Chile saltpeter and other nitrates is based on the following principles:[180]
(1) If a nitrate be heated in contact with sulfuric and phosphorous acids, nitrous acid will be formed.
(2) If nitrous acid be boiled with ammonium chlorid, nitrogen will be quantitatively evolved from both compounds. These processes are illustrated by the following formulas:
(a) N₂O₅ + P₂O₃ = N₂O₃ + P₂O₅.
(b) N₂O₃ + 2NH₄Cl = 2N₂ + 3H₂O + 2HCl.