FOOTNOTES:
[97] As the formation of nitrites is a stage in the process, the term nitrification includes the formation of nitrites as well as nitrates.
[98] Nitre seems to have been known as early as the thirteenth century.
[99] Lawes and Gilbert, for example, have shown that in the Rothamsted soils it only amounts to a few parts per million of soil.
[100] See Appendix, Note I., p. 196.
[101] The artificial production of nitre seems to have been first effected by Glauber in the seventeenth century.
[102] The lime-rubbish from old buildings, especially those parts which have come in contact with the earth, or plastering from the walls of damp cellars, barns, stables, &c., have been found to be rich in nitrate of lime, and, as has been long well known, constitute by themselves a valuable manure. The formation of the nitrate of lime can be accounted for by the contact of the lime with nitrogenous matter of different kinds.
[103] As much of the nitric acid in this solution was present as nitrate of lime, it was usually treated with a solution of potassium carbonate, the result being the precipitation of the lime as carbonate, pure saltpetre being left in solution, according to the following equation—
K2CO3 + Ca(NO3)2 = 2 KNO3 + CaCO3.
Under the French mode of manufacture, the process was considered to have developed satisfactorily when 1000 lb. of earth, at the expiration of two years, yielded 5 lb. of nitre.
[104] Pasteur had already in 1862 expressed the opinion that nitrification might probably be in some way connected with ferments. A. Müller (see 'Journal of Chemical Society,' 1879, p. 249) was the first to advance the opinion that nitrification was due to the action of a ferment. This conclusion he was led to by the observation that while the ammonia in sewage was converted into nitric acid, no change took place in solutions of ammonia or urine prepared in the laboratory.
[105] Bisulphide of carbon and phenol (carbolic acid) have also been experimented with in connection with their antiseptic action on nitrification. In these experiments the former had a similar effect to chloroform; the phenol, however, while hindering it did not entirely suspend it, due probably to the difficulty of bringing the phenol vapour into thorough contact with the soil-particles.
[106] Winogradsky has named the nitrous organism nitrosomonas, and the nitric organism nitrobaeter.
[107] From a series of Lectures delivered by him in connection with Lawes Agricultural Trust, in the United States.
[108] This silica-jelly consists of dialysed silicic acid, ammonium sulphate, potassium phosphate, magnesium sulphate, calcium chloride, and magnesium carbonate.
[109] This fact is all the more striking when we remember that this decomposition of carbonic acid is best effected in the dark, since light is prejudicial to nitrification.
[110] See Appendix, Note II., p. 196, and Note III., p. 197.
[111] See Appendix, Note V., p. 198.
[112] This is shown by the fact that nitrification will only continue in a solution of carbonate of ammonia till one-half the ammonia is nitrified. It then stops. The base, with which the nitrous acid combines as it is formed, being at that stage entirely used up, nitrification is no longer possible. With regard to urine solutions the same is the case. Nitrification thus will only take place where there is a sufficiency of base.
[113] See Appendix, Note IV., p. 197.
[114] It would seem that an alkalinity much exceeding four parts of nitrogen per million is prejudicial to the process.
[115] According to Warington, solutions containing 50 per cent of urine become nitrifiable when sufficient gypsum is added. The gypsum neutralises the alkalinity of nitrifying solutions by converting the alkaline ammonium carbonate into neutral ammonium sulphate, the calcium carbonate being precipitated.
[116] See Chapter on Farmyard Manure.
[117] As practically illustrating this fact, a solution kept at 10° C. required ten days, while a solution kept at 30° C. required only eight days for nitrification.
[118] In sixty-nine trials no failure to produce nitrification by seeding with soil from a depth, of 2 feet was experienced. Similarly in eleven trials only one failure took place with soil from a depth of 3 feet. With clay soil from a depth of 6 feet success took place to the extent of 50 per cent. No nitrification was obtained with clay from a depth of 8 feet. Entire failure was experienced with chalk subsoil. The process thus diminishes in activity the lower down we go.
[119] Koch has found that in soils he has examined few organisms were found at a depth below 3 feet.
[120] See Appendix, Note VI., p. 198.
[121] For full analytical results see Appendix, Note VII., p. 198.
[122] We find the least amount in the month of April. In the water, from a 20-and 60-inch gauge respectively, the amounts were 1.35 lb. and 1.61 lb. per acre (rainfall 2.25 inches). From then on to November the amount steadily increases. In the latter month it reaches its maximum—viz., 6.50 lb. (20-inch gauge) and 5.98 lb. (60-inch gauge) per acre (rainfall 2.30 inches). See Appendix to Chapter III., Note VIII, p. 160.