THE lONISATION OF THE AIR. 27I 



average mobilities of the first and second class of ion respec- 

 tively. Hence, during the actual observations both these types 

 of ion must have been present. Thus an average mobility of 

 .058 would indicate the presence of a large number of the larger 

 of these ions and only a few small ions. An average mobility 

 of .736, on the other hand, would suggest an important diminu- 

 tion in the number of the larger ions, and hence a diminution in 

 the total number of ions per c.c. We should therefore expect 

 to find associated with low average mobilities high values for 

 the total number of ions, and vice versa. 



If the Gerdien and Ebert instruments are to give results 



C V . 

 that are at all comparable, the quantity^y^ derived above must 



be chosen of the same order for both. With the present designs 



of apparatus this is almost impracticable. Thus, in the case of 



C V 

 the Gerdien the value of -^ - could be made to approxmiate to 



that for the Ebert by reducing V and increasing A''. The design 



of the Gerdien electroscope, however, does not admit of any 



important reduction of T'. while the large dimensions of the 



outer cylinder make it difficult to increase A^ beyond lOO c.c. per 



sec. On the other hand, a decrease in A'' in the case of the Ebert 



is not convenient ; while the range over which V can be varied 



C V 

 is again limited. I have brought the quantity —^ for the Ebert 



apparatus nearer the corresponding quantity for the Gerdien by 

 increasing the capacity of the Ebert with the help of a parallel 

 plate air condenser ; and values given by the instrument so modi- 

 fied certainly approach those given by the Gerdien. Unfortu- 

 nately, the increased capacity of the Ebert, reducing as it must 

 the rate of leak of the electroscope, has the eft'ect of greatly, 

 and probably prejudicially, extending the time required for 

 making the necessary observations. 



Soluble Phosphates. — Prof. W. Bottomley has 



patented a novel process for the manufacture of soluble phos- 

 phates for fertilising the soil. The specification claims the manu- 

 facture of soluble i)hosphate from mineral phosphate by mixing 

 the finely sub-divided phosphate with a small proportion of a 

 suitable food for micro-organisms, and with aerobic organisms 

 from putrefying organic matter, and maintaining the mixture 

 at a temperature considerablv above the normal. It is also 

 claimed that the soluble phosphate may be produced from mineral 

 phosphate by moistening the latter, after having been finely sub- 

 divided, with a putrefying liquor, and maintaining the mass at 

 about 30 degrees Centigrade for about a week. 



