Commercial Fertilizers. 157 



soluble forms. This substance contains from 2 to 3 per cent of 

 nitrogen and 15 to 17 per cent of available phosphoric acid. It 

 will be seen that in respect to its nitrogen content it differs ma- 

 terially from dissolved rock or acid phosphate, which does not 

 contain this element. The term "dissolved bone" is often used 

 in speaking of "dissolved rock," as for example, "dissolved 

 South Carolina bone." This use of the term is incorrect, as 

 there is no bone in South Carolina rock phosphate. 



Basic slag, also called "Thomas slag," or "odorless phos- 

 phate," is a by-product in the manufacture of iron and steel 

 from pig iron containing phosphorus. It contains from 15 to 20 

 per cent of phosphoric acid in a form differing slightly from the 

 phosphates already discussed. In this material there are five 

 parts of lime combined with one part of phosphoric acid. The 

 material is insoluble in water, but readily soluble in saline solu- 

 tions. From the results of numerous experiments it has been 

 found that this material has a high degree of availability, about 

 equal to one-half that of a soluble phosphate. Its value as a 

 fertilizer partly depends upon its fineness of division. The finer 

 it is ground the more quickly it will become available. The fact 

 that it contains a high lime content has made it particularly de- 

 sirable for acid soils, on which it has given excellent results. 



Guano. Many mixed fertilizers and fertilizing materials are 

 incorrectly spofcen of as " guano. ' ' The term^hpuld be applied to 

 the natural product only, which consists of the excrement and 

 remains of sea fowls, and which have accumulated in certain re- 

 gions along the coast of South America and on some of the is- 

 lands in the Carribean sea. There are two kinds, dependent upon 

 the conditions under which they were formed. When the forma- 

 tion took place in a dry warm region, the excrement dried quick- 

 ly and remained practically unchanged. This will contain all 

 the nitrogen, phosphoric acid and potash originally in the 

 manure. Some of the early guanos contained as high as 20 per 

 cent of nitrogen, but those now on the market are of poorer 



