230 CHEMICAL FERTILIZERS 



fertility, there is much land which has received so little 

 fertilizer that it is still going back. It is on the latter very 

 hungry soil that insoluble phosphates will produce their 

 best results ; when the land has acquired a certain condition 

 of fertility, it will no longer respond to the insoluble forms, 

 although it may show excellent results from the application 

 of soluble forms of phosphate. It is also certain that mix- 

 tures of nitrogen, partly soluble and partly insoluble, are 

 often better than either alone, although there is no evidence 

 to show that in the case of potash the value of the insoluble 

 forms is more than a small fraction of that of the soluble 

 forms. In the construction of compound fertilizers it would 

 be advantageous if these materials were better standardized 

 than they are at present. Simple mixtures containing the 

 fertilizing ingredients in proportions of round numbers 

 would be better than the odds and ends one often sees quoted. 

 Standard articles containing, say, i or 3 % of soluble nitrogen, 

 i or 2 % of insoluble nitrogen, 10 % of soluble phosphates, 

 10 % of insoluble phosphates, and I, 2 or 3 % of potash would 

 serve practically any ordinary purpose. If half a dozen 

 standard formulae with even numbered percentages were 

 devised by the manufacturers, it would add much to the 

 popularity and utility of such materials. Fancy names are 

 only misleading, if they attract the ignorant man they repel 

 the intelligent farmer. 



Some very marked improvements in manufacture are 

 likely to follow on the recent engineering successes in the 

 recovery of dust of all descriptions. Among the numerous 

 methods that have recently been employed for separating 

 solid and liquid substances from gases which hold them in 

 suspension, may be mentioned the electrical precipitating 

 process designed by Cottrell. If a metallic plate connected 

 to one terminal of a source of high potential is fixed opposite 

 to a needle point, connected to the other terminal of that 

 source, the air particles in the gap will take up a charge of 

 electricity. The solid and liquid particles floating in the gap 

 also become electrified, and are attracted to the plate elec- 

 trode. The greater the potential difference, the higher the 



