394 PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 



ledge that there should be a marked difference in accessibility 

 to the plant of those contained in Guano, Bones, and Coprolites, 

 or other mineral phosphates. In the first of these forms the 

 phosphate of lime is in a state of subdivision far exceeding any- 

 thing which can be obtained by mechanical processes ; in 

 bones they are less highly divided ; while in coprolites or other 

 mineral forms they are in so compact a condition as to present 

 great resistance to solution, either by the active constituents of 

 the soil, or by the roots, by whichever of these agents it may be, 

 that they are brought into an assimilable condition. The 

 difference between phosphates in these three states is sufficiently 

 seen if small quantities of a guano previously burned to destroy 

 organic matter, of bone-ash and of ground coprolites, be treated 

 with the same acid. The first is found to dissolve in a very 

 short time, the second requires considerably longer, and the 

 phosphates of the third may be but imperfectly dissolved even 

 after some hours. But it is quite otherwise when the phosphates 

 have been dissolved. Chemistry then recognises no difference 

 between them, and the source from which they have been derived 

 can only be determined by ascertaining the nature of the im- 

 purities which may have been associated with them. With 

 these facts before him, the chemist is led to conclude that soluble 

 phosphates, from all the different sources, ought to have the 

 same manurial effect, and to advise the farmer, when he wishes 

 to make use of them, to take those which he can obtain at the 

 cheapest rate. He, on the other hand, is naturally desirous that 

 these opinions should be confirmed by actual experiment in the 

 field, and to do this was one of the objects of the enquiry now 

 to be recorded. 



A similar question may be raised in regard to the different 

 forms in which nitrogen is used as a manure. We know well 

 that, in order to enable that element to maintain the growth of 

 plants, it must be used in the form of some compound, among 

 which ammonia is recognised as one of the most important, as it 

 is also the simplest. But in bones, rape dust, and other 

 similar substances that element is found in much more 

 complex compounds, which must be decomposed and con- 

 verted into ammonia before it becomes available to the crop. 

 It is well known that these compounds do decompose in the 

 soil, but the question remains whether the necessity for under- 

 going this transformation, before they become useful, may not in 

 some cases so retard their action as to render them less valuable 

 to the farmer than the ready formed ammonia. To this the 

 chemist working in the laboratory can give no answer, because 

 he has not the means of ascertaining how rapidly the conversion 

 of these substances into ammonia takes place. That this change 

 does occur is well known, and he may hazard the opinion that 



