208 Mr. Hall, Dr. Miller, and Mr. Gimingham. __[ Dec. 19, 
Again there was no formation of nitrates except when the acidity of the 
medium had been neutralised by the calcium and magnesium carbonates. 
Flask 4 showed a heavy crop of moulds in fructification, 7 and 8 showed 
mycelium in the liquid, 10 one or two colonies of a bacterium on the surface. 
D. The Nature and Extent of the Acidity. 
Fresh soil to the depth of 9 inches was taken in March, 1907,a month after 
the application of the ammonium salts, and about 7 kilogrammes of the soil 
as it came from the field was extracted on a pressure filter with successive 
portions of hot water. No attempt was made to remove all the acid, as 
previous trials had shown this to be impossible with water alone; the soil 
after extraction still reddened blue litmus paper. The extract showed an 
acidity equivalent to 1°71 grammes hydrogen per million of dry soil. 
Sulphates and chlorides were also determined in the extract as follows :— 
Chlorides equivalent to 1:91 grammes hydrogen per million soil. 
Sulphates ~ Br Os) n 
When the soil was extracted with a fifth normal solution of sodium 
chloride, the acidity of the extract amounted to 30 grammes hydrogen per 
million of dry soil; substituting potassium nitrate for the sodium chloride, 
the acidity was equivalent to 42°5 grammes hydrogen per million of dry soil. 
In these two latter cases humic acid, insoluble in the water extract, was also 
being estimated. 
Another sample was taken in November, 1907, and extracted in the same 
manner with the following results :— 
Acidity equivalent to 1:02 grammes hydrogen per million soil. 
Chlorides A 0°35 3 i 
Sulphates ¥ 1°60 i a | 
At this latter date a sample was taken from Plot 9 and gave the following 
results :— 
Acidity equivalent to 0°36 grammes hydrogen per million soil. 
Chlorides a 0°47 » ” 
Sulphates a 1:69 is 9 
In this case some of the humic acids dissolved in the original extract were 
thrown out during the evaporation of the extract, hence the acidity measured 
is a little low. The acidity of the soil persists after drying in the air, but 
is measurably reduced when the soil is dried in the steam oven. 
If these measured acidities are calculated on the proportion of water usually 
found in the soil, which will vary between 10 and 25 per cent. of its dry 
weight, the following results are obtained :— 
