AGEICULTURAL CHEMISTEY AGROTECHNY. 303 



The conclusions from this worli are as follows : " ' Humic acid ' was pre- 

 pared by two methods, with ammonia and with sodium hydroxid and sodium 

 phosphate. Humic acid shaken with salt solution according to Hopliins' method 

 for soil acidity (E. S. R., 14, p. 1045) exhibits only about 12 per cent of its 

 real acidity." The authors also point out that the humates do not behave 

 toward precipitating agents as in ordinary reactions but almost always require 

 an excess of the reagent before the precipitation occurs, and further that a 

 difference exists in the humates obtainetl from various soils. 



" Magnesium salts do not precipitate some humates, and magnesium humate 

 is much more easily soluble in water than calcium humate. Humic acid is 

 dissolved by caustic soda in presence of calcium carbonate. Analyses of 

 humic salts gave an equivalent [combining weight] of about 2.50 for the 

 mixed humic acids. Humic acid boiled with hydrochloric acid gave about 

 2 per cent reducing sugars. The humus preparations contain easily diffusible 

 material, when dissolved in ammonia. After 2 or 3 diffusions, the ' ammonium 

 humate ' diffuses at the nearly constant rate of about 1 to 2 per cent of the 

 humate. The quantity of phosphoric acid in the humus preparations by 

 ammonia varies from 0.13 to 0.54 per cent, which is a small amount. The 

 purified humic acid (by ammonia) contains 44 to 5G per cent carbon and 4.3 

 to 5.4 per cent nitrogen. Humic acid extracted by phosphate contains a high 

 amount of ash. The water and ash-free material contains 52 to 64 per cent 

 carbon and 3.7 to 5.2 per cent nitrogen. The humic acids from the California 

 soils are not rich in nitrogen. Humus soluble in alcohol contains higher per- 

 centages of carbon than that not soluble. The clay precipitated by ammonium 

 salts from the humus solution contains from 1.53 to 7.80 per cent carbon, 

 equivalent to 2.64 to 13.45 per cent organic matter. The suspended clay may 

 thus contain considerable percentages of organic carbon. The loss on ignition, 

 less the organic matter, varies from 1.77 to 13.04 per cent of the clay. The 

 average is 8 per cent. This is the amount of the correction which should be 

 made, if any is to be made." 



The ammonia in soils, E. J. Russell {Jour. Agr. Sd., 3 {1910), A'o. 5, pp. 

 233-2.'f5, flgs. 2). — The author for the purpose of this worlv considers a sub- 

 stance an ammonia compound if it evolves ammonia quicklj", completely, and 

 in one stage, when treated with alkalis at a low temperature. 



" When soils are distilled at low pressures with small quantities of potash 

 dissolved in alcohol, a definite amount of ammonia is evolved and the reaction 

 then comes to an end. It is considered that this amount represents the am- 

 monium salts in the soil. When larger quantities of potash are used, or 

 when baryta or magnesia in aqueous suspension is substituted, the decom- 

 position is not definite but continues indefinitely. During the progress of the 

 first distillation, however, magnesia gives off the same quantities of ammonia 

 as small quantities of alcoholic potash. 



" Two methods based on these observations are given for estimating the 

 amount of ammonia in soils. If the amount of organic matter is not too 

 high distillation with magnesia at reduced pressure gives accurate results, 

 otherwise it is necessary to use alcoholic potash. The quantity of ammonia 

 in samples of soil taken at different periods of the year is found to be con- 

 stant but very small, being only about one or two parts per million of soil. 

 The higher the amount of organic matter the greater the ammonia content, 

 rising to five or six parts per million on heavily dunged arable or garden soils. 



"As there is no tendency for ammonia to accumulate it follows that the rate 

 of nitrification must be greater than that of ammonia production and in 

 normal conditions is limited by this rate. Reviewing in the light of this 

 observation the various methods of studying the rate of nitrification in soil, 



