NEW SOURCES OF FERTILIZERS 227 



these lines should form part of any future national agri- 

 cultural policy. lyarge quantities of nitrogen can be fixed 

 in this way, but the nitrogen is not in a very active form, and 

 soluble nitrogen compounds will still be necessary for farming 

 practice. Chemical nitrogen fertilizers will always have the 

 great advantage of serving as a top dressing during critical 

 periods. 



Phosphates. Future discoveries of phosphatic manures 

 may be looked upon as almost certain. Ultimately, further 

 developments in the steel industry will produce an increasing 

 amount of basic slag. There is a tendency to use ores con- 

 taining little phosphorus at first, but as these become ex- 

 hausted, poorer ores are consumed, which yield larger amounts 

 of phosphatic slag. No very great improvement in the 

 manufacture of slag can be anticipated from the fertilizing 

 point of view ; the general tendency has been to produce 

 basic slag of decreasing solubility. There is some reason to 

 believe that a finer degree of grinding may compensate for 

 the decreasing solubility of these materials. 



Potash Fertilizers. Very promising sources of potash 

 for the future are the flue gases and dusts of blast furnaces, 

 cement kilns, and other industrial operations conducted at 

 very high temperatures. The Scottish blast furnaces, being 

 mostly coal fired, produce less potash than the English coke- 

 fired furnaces. The replacement of coal by coke would 

 result in the increased production of potash. It has been 

 found that by increasing the temperature of the furnaces, 

 or by adding common salt, the amount of potash volatilized 

 is increased many-fold. It seems highly probable that some 

 of the potash which is produced in the blast furnaces comes 

 from the fuel, in which case enquiry should be made into 

 the potash contents of all the different fuels. This is a 

 matter which has hitherto attracted no attention, but the 

 substitution of fuel containing much potash for one contain- 

 ing little, might produce a profound result on the potash 

 yield. The potash from vegetable and kitchen refuse might 

 be rendered available if destructors were modified for the 

 purpose. Wool washings can provide an appreciable amount 



