SOILS AND FERTILIZERS 517 



other reasons superphosphates may not work as well on acid muck 

 or peat soils as ordinary undissolved phosphate rock or ground bone, 

 and if, as is sometimes the case, a slight excess of sulphuric acid is 

 present they may even have a temporary injurious action upon 

 upland soils which are deficient in carbonate of lime. 



Basic slag (Thomas slag or slag meal) is a waste product ob- 

 tained in the manufacture of steel. It contains relatively more lime 

 than the ordinary high-grade phosphates, and the phosphoric acid 

 in most cases (a few works have put an inferior product on the Euro- 

 pean market) is possessed of a high degree of assimilability. This 

 product is as yet too little known in this country, and if sold here as 

 cheaply as it might be it would doubtless prove of great value to our 

 agriculture. It is an effective source of phosphoric acid for use upon 

 all kinds of soils, and on account of its high percentage of lime it is 

 of special promise in the reclamation not only of acid upland soils, 

 particularly if rich in organic matter, but also of marsh or muck 

 soils. 



Unleached wood ashes contain about 35 pounds of actual lime 

 (calcium oxid) in every hundred, 3 tons being, therefore, a little 

 more than equivalent, in lime, to 1 ton of burned lime. They also 

 contain from 5 to 7 per cent of potash, 1 to 2 per cent of phosphoric 

 acid, and from 3 to 5 per cent of magnesia. This latter ingredient, 

 though usually ignored, is of approximately as much value as lime 

 on acid soil. Soils are sometimes deficient in magnesia, and when 

 this is the case the magnesia applied in ashes has a direct manurial 

 action. 



Leached wood ashes contain usually less than Iper cent of pot- 

 ash and rather more lime than unleached ashes. Frequently they 

 are sold in a wet condition, which of course lessens the quantity of 

 actual lime present in a ton. 



Limekiln ashes often contain approximately 40 per cent of lime, 

 and when wood is employed in the burning instead of coal they 

 sometimes contain 2 per cent or more of potash. 



Finely ground limestone and oyster shells can be used to ad- 

 vantage, if obtainable, especially upon sandy soils. They are not as 

 efficacious as after burning upon heavy clay soils and such soils as 

 are very acid and contain large amounts of sour humus. This is for 

 the reason that they are not so active chemically, and they can not 

 be reduced to so fine a state before burning as afterwards. 



Dye-house lime usually contains only a small percentage of 

 lime, and if moist can not be transported long distances at a profit. 

 A rule that applies well to this and all other waste products of a sim- 

 ilar character is riot to use them until they have been subjected to v 

 chemical analysis, for by changes in the processes of manufacture 

 their value may be materially influenced and substances injurious to 

 vegetation may have found access to them. 



Gas-house lime. It is never safe to use this substance until it 

 has first been allowed to weather for several months. On acid soils 

 such lime is less effective than burned lime, wood ashes, and limekiln 



