[123] Perhaps the liberation of nitrous gas from the solution takes place at a lower temperature than its decomposition. I have always observed that the quantity of yellow precipitate is greater when the solution is rapidly made to boil. Were it possible to heat it to a certain temperature at once, probably a compleat decomposition would take place.
[124] Annales de Chimie. T. 38, pag. 187.
[125] Annales de Chimie, xxiii. pag. 85; or Nicholson’s Phil. Journal vol. i. pag. 45.
[126] Probably by giving them oxygene; whereas the green muriate and sulphate blacken animal substances; most likely by abstracting from them oxygene.
[127] The existence of green nitrate was not suspected by Proust.
[128] In this process nitrous oxide is sometimes given out, as will be seen hereafter.
[129] Hence we learn why no nitrous gas is disengaged when impregnated solution of sulphate of iron is decomposed by prussiate of potash, as in Div. IV. Sec. vii.
[130] In both of these solutions the metal is at its minimum of oxydation. The absorption of a small quantity of nitrous gas by white vitriol was observed by Priestley.
[131] Humbolt, who is the first philosopher that has applied the solution of sulphate of iron to ascertain the purity of nitrous gas, asserts that he uniformly found nitrous gas obtained from solution of copper in nitrous acid, to contain from six tenths to one tenth nitrogene.
Annales de Chimie, vol. xxviii. pag. 147.