1907. | | Nitrification in Acid Sorls. 209 
Approximate Acidity of Soil-water. Fractions of normal. 
When soil contains 10 per When soil contains 25 per 
cent. water. cent. water. 
Plot 11-1, March, 1907 ...... 1/60 1/150 
Plot 11-1, November, 1907... 1/100 1/250 
Plot 9, November, 1907 ...... 1/300 1/700 
To ascertain if the acid soils contain any free humic acid, 10 grammes 
of the soil of Plot 11-1 were extracted with 500 c.c. of 4-per-cent. ammonia 
solution, and the amount of organic matter going into solution was determined. 
On a second 10 grammes the usual process of determining “humus” was 
followed; the soil was treated with hydrochloric acid, and the acid washed 
away before extracting with the ammonia solution. Parallel experiments 
were made with a prairie soil rich in humus but neutral, since it contained 
35 per cent. of calcium carbonate. The following results were obtained :— 
Organic matter soluble in ammonia. 
ae a age ae 
Without acid After preliminary 
treatment. acid treatment. 
IPOD RISD, o. «us cessentnates oath 3°54 per cent. 4°51 per cent. 
PPAITIO OSE Lod cacescecvedeetaee Nil 4°65 
The prairie soil yielded no humic acid to ammonia, unless the humates 
it contained had first been decomposed by hydrochloric acid, whereas the 
soil of Plot 11-1 contained 3°54 per cent. of humic acid immediately soluble 
Im ammonia. 
EK. Lnberation of Acid from Ammonium Salts. 
To ascertain if any of the organisms in the soil of these acid plots were 
capable of setting free ammonia from its salts, small Erlenmeyer flasks, 
containing a solution made up of 2 grammes ammonium chloride, 0°5 gramme 
monopotassium phosphate, 0°25 gramme magnesium sulphate, 1 gramme 
sodium chloride, and 10 grammes of glucose per litre, were sterilised, 
inoculated with the soil or soil extract, and incubated at 21° C. After 
seven days a vigorous growth of various moulds was observed, and the 
medium was found to be distinctly acid. In mixed cultures of this kind 
the acidity rose from about 1/166 to n/80 in a week, and then remained 
constant. Sub-cultures were made and the organisms isolated in the 
usual way: the dominant species were forms of Penicilliwm glauweum and 
a Mucor(?), which differs in several respects from those already known, and 
does not appear to have been described.* Samples taken from Plots 11-1, 
9, and 4-2 at different times during the spring and summer showed the 
same dominance of Penicilliwm and the Mucor. Various other species of - 
* This mould has since been identified by Professor A. F. Blakeslee as Zygorhynchus 
Moeller, Vuill.—Note added March 19, 1908. 
