• 146 ANNUAL REPORT OF THE Uft. Doc. 



PROF. McDowell : Of course, as far as phosplioric acid is con 

 cerued, as a chemical element, it is phosphoric acid; it doesn't mat- 

 ter at all from what source it is derived. Phosphoric acid is con- 

 tained, as I said a little while ago^ in different forms in these various 

 forms of phosphate; it is contained in exactly the same form in the 

 bone or in the rock. 



A Member: What proportion of phosphoric acid is there in roasted 

 bone? 



PROF. McDOWELL: That depends upon the condition of the 

 roasting; it would probably contain as high as thirty or even more 

 per cent. The roasted bone would probably contain a larger per- 

 centage, depending upon the extent to which that process had been 

 carried on. 



A Member: I ask these questions because I can produce it from 

 a mill that I have, and it is a question with me whether I can afford 

 to buy it in preference to buying the ground bone, when I have a 

 bone at home at a nominal price. 



PROF. iMcDOW^ELL: In roasting the bone you get rid of that ma- 

 terial I speak of that makes it difficult to grind. The only thing is^ 

 if you roast it to too great an extent, there is danger of rendering 

 it more insoluble than in the raw state. 



A Member: What is the origin or source of phosphoric acid? 



PROF. McDOWELL: 1 don't know that I understand just what is 

 meant by that question; the original form was probably in the form 

 of bone. Is that what you had reference to? 



A Member: Is there any difference in the value of bone dissolved 

 with sulphuric acid or with acid from gas works? 



PROF. McDOWELL: W^ell, of course, any acid will have the sani* 

 dissolving effect upon bone. There are other acids which will pro 

 duce the same effect, bring about the same result as sulphuric acid, 

 but sulphuric acid is the one that is most convenient to use in prac 

 tice. 



A Member: Will a soil overrun with sorrel ad as a solvent on 

 fertilizers that may be present? 



PROF. McDOWELL: Soil overrun with sorrel — ^^L•!I, sorrel i> 

 sometimes an indication of a sour condition; that is not necossaril;> 

 so. If the soil is acid, of course that acid will have a tendency U^ 

 act upon any insoluble material in the soil. 



A Member: Does it make any difference to plants from what sourc«' 

 the different elements of plant food in the commercial fertilizer u]> 

 plied to the soil is derived. 



PROF. McDOWELL: Yes, it does sometimes. Take potash, for 

 instance, in the form of muriate. It is claimed that potash in tin 



