232 SOILS 



tanks and boiled that the albuminoids may be coagulated. 

 The water of this material is then removed ; the resulting 

 materials are pressed into cake, and later broken, and 

 dried, and ground all operations essential in making the 

 commercial product. 



Tankage. This is a by-product of the slaughter-house 

 and contains from four to eight per cent, of nitrogen and 

 from seven to fourteen per cent, of phosphoric acid. It 

 slowly decomposes in the soil, and is generally appre- 

 ciated as a chemical fertilizer. Included in this product 

 are intestines, lungs, tendons, bones, blood, and other 

 refuse. After being cooked in tanks and pressed, it is 

 dried and ground, and then is sent out as a fertilizer or 

 as a feeding stuff for pigs. 



Dried and ground fish or dried fish scrap, as it is 

 often called is a by-product of the fish-oil and canning 

 factories. Both nitrogen and phosphorus are contained in 

 this product: from six to eight per cent, of the former, 

 and from seven to nine per cent, of the latter. This by- 

 product is consumed largely by those near the sources of 

 supply. 



Cotton-seed meal. Usually about seven per cent, of 

 nitrogen, or one hundred and forty pounds to the ton, are 

 found in this fertilizing material. It is by far the most 

 important of the vegetable products used as commercial 

 fertilizers. It decays somewhat rapidly, yet lasts long 

 enough so that the growing crop may use it. It is more 

 promptly available than tankage, but much less quickly 

 available than either nitrate of soda or sulphate of am- 

 monia. 



Cotton-seed meal is a by-product of the cotton-oil mill. 

 In removing the oil from cotton seed, the seed are cut into 

 bits and cooked and pressed into cakes. These cakes are 

 then ground into fine meal, which may be used either a 



