104 



From this table it will be noticed that when the Cadmium cells are first set 

 up they differ somewhat in E. M. F. But after about a month they come to have 

 a normal value which is common to all. Moreover, this value is not affected by 

 any moderate change in temperature, and so far as our experience goes, these cells 

 are more easily made, and there is less variation in E. ]\[. F. between them than 

 there is between the Clark cells. 



It will be noticed that the values given in Table Xo. 1 are simply relative, 

 but we have made absolute determination of their E. M. F. , and tind for the Wes- 

 ton cell the value 1 OlSol volts when the resistance is measured in Legal ohms; or 

 1.01o(j3o volts when the resistance is measured in International ohms. 



The result of our investigations lead to the following conclusions: 



Fii-M. That the Cadmium cell is more easily constructed than the Clark cell. 



Second. That it has practically no temperature coetticient. 



Third. That the E. M. F. of the Cadmium cell is even less variable than that 

 of the Latimer Clark. 



Soil Solvents for Available Potash and Phosphoric Acid. By H. A. 

 Huston and .J. M. Barrett. 



It seems to be accepted that in the case of worn soils solution in strong min- 

 eral acid gives little insight into the availability of their potash and phosphoric 

 acid. More recently the use of dilute organic acids, such as the one per cent, cit- 

 ric acid used br Dr. Bernard Dyer^ and the acid ammonium oxalate used by Dr. 

 A. M. Peter-, has been tiied with more promising results. The theory of the use 

 of dilute organic acid solutions seems to rest on the idea that plant roots give 

 off fluids containing organic acids which act on the soil in a degree comparable 

 with the effect of the dilute acids employed in the laboratory experiments. 



While I do not question that plant roots in contact with polished marble, or 

 even granite, may make appreciable markings on the carbonate of lime and on 

 the feldspar of the granite, the conditions of the experiment, as usually conducted, 

 differ radically from those found in the field, for in the experiment the plants are 

 not supplied with normal soil water. So far as I have observed, normal soil 

 waters give an alkaline reaction. No inconsiderable part of the food of the plants 

 comes to it dissolved in the soil waters. The work of Dr. H. J. Wheeler* shows 

 what marked difficulty is encountered in growing plants on a well-drained soil 

 having an acid reaction. 



