17 



There are other substances furnishing phosphoric acid in varying 

 quantities such as tankage, fish, guanos, etc., but these are usually 

 bought for their nitrogen content. The phosphoric acid which they 

 contain, however, is more available, when used in the unacidified 

 condition, than is the phosphoric acid from the natural or mineral 

 phosphates. This is due to the fact that more or less organic matter 

 is associated with the bone and as this decomposes in the soil the 

 bone gradually yields its phosphoric acid. Probably from three to 

 five years are required for all of it to become active, depending to a 

 great extent upon the fineness with which it is ground, 



Owing to numerous inquiries regarding basic slag and to the fact 

 that it is a comparatively new product in our local markets, the fol- 

 lowing brief statement is submitted. 



Phosphatic or Thomas slag is a by-product in the modern method 

 of steel manufacture from ores containing noticeable quantities of 

 phosphorus. The process of removing the phosphorus from the ore, 

 briefly stated, consists in adding to the so-called converter containing 

 the milled ore, a definite amount of freshly burned lime which, after 

 a powerful reaction, is found to be united with the phosphorus and 

 swims upon the surface of the molten steel in the form of a slag. At 

 the present time, according to Wagner, practically all of the iron 

 works treat the molten slag as it flows from the converter with hot 

 quartz sand, with the result that the availability of the phosphoric 

 acid is increased from lo to 30 percent.' 



The principal constituents of the slag are phosphoric acid, 

 lime, iron oxides and silicic acid. It is placed upon the market iri 

 the form of a dark brown powder. Its phosphoric acid was formerly 

 supposed to exist in the form of tetra-calcium phosphate, but the 

 opinion is now generally held, especially by Wagner, that the phos- 

 phoric acid is combined in the slag as a double salt of calcium 

 phosphate and calcium silicate, and that in this form the roots are 

 able to utilize it. 



The slag has been found to work especially well upon sour marsh 

 and meadow lands, upon porous, well-aired soils rich in humus, as well 

 as upon sandy soils deficient in lime. The usual amount per acre is 

 from 300 to looo pounds. 



1 Dungungsfragen, Heft 1, p. i6 von P. Wagner 1S96: also Anwendung Kuntsliche Dunge- 

 mittel, vierte Auflage von Wagner, p. 74-75. 



