478 



Basic Slag. 



[NOV., 



infected ; (2) To the presence of fungus spores in the land ; 

 this implies the previous presence of a diseased crop in the 

 same soil. 



Under the circumstances, preventive measures will consist in 

 not planting " sets " grown in an infected area ; where the 

 disease has occurred the haulms should be brought together and 

 burned. As the above-ground portion of the potato plant can- 

 >not be infected, spraying would be of no avail, unless, as claimed 

 by some, spraying invigorates the plants and better enables 

 them to combat the disease. 



A dressing of kainit in the rows when the potatoes are 

 planted would to a certain extent safeguard the crop by killing 

 the fungus spores present in the soil at the moment of ger- 

 mination. 



Basic slag is a by-product in the manufacture of steel, and 



its composition is not regulated by the manufacturer as is the 



case with, say, superphosphate. Iron ores 

 . Basic Slag. . y \ v F _f f , , 



contain irregular quantities 01 phosphorus 



(the substance which gives to the phosphate of lime found 



in bones and some other manures its value as a fertiliser), and 



the object of the steel-maker is to get rid of all the phosphorus 



in the iron. To effect this the iron is melted in contact with 



limestone, which extracts the phosphorus and forms a slag. 



This, when ground to a fine powder, is basic slag, which may 



vary very considerably in quality, the usual contents being 



30 — 40 per cent, of insoluble phosphate, though there may be 



as little as 22 per cent., or as much as 45 per cent. 



In an experiment carried out by the Agricultural Department 



of the University of North Wales, Bangor, in 1898 and the three 



succeeding years with different qualities and quantities of basic 



slag, it was found that the low-grade slag gave as good results 



as the more costly higher-grade slag, particularly where a large 



dressing per acre was applied. It has been maintained by 



Wagner, as a result of his work on basic slags, that only the 



phosphoric acid which is soluble in a weakly acid solution, such 



as a 2 per cent, solution of citric acid, is of value for manurial 



