E. J. Russell and J. A. Prescott 



71 



which though very flat do not appear over any part of their course to 

 be straight lines. There is no sign of any break in the curves, and 

 nothing to indicate any definite stages in the reaction (Fig. 2, Table III). 



Hoos 2C Soil 



•05 -10 -15 



Initial acidity, equivalents HNO3 per litre 

 Fig. 2 e. 



2. All dilute acids, as far as they have been examined, give curves 

 of the same type. The amount of action, however, varies in a remark- 

 able manner, the strong acids such as hydrochloric and nitric being 

 less potent than equivalent concentrations of the weaker citric and 

 oxalic acids. At N/10 concentration hydrochloric and nitric acids 

 behave very similarly and bring out less phosphate than N/10 sulphuric 

 acid: this in turn brings out less than N/10 citric acid, while N/ 10 

 oxalic acid gives the highest results of any. 



3. When curves obtained for different periods of time are plotted 

 together they are seen to be very much alike, but they do not all lie 

 parallel to one another : there is a certain amount of crossing, i.e. the 

 amount of action is not proportional to the time. At the beginning 

 of the curve, where the concentration of the acid is nearly N/20, the 

 action usually shows the remarkable peculiarity that it is less after 

 24 hours than after 10 minutes. Beyond certain concentrations. 



