EXPEEIMENT STATION. 39 



" Potato Manure," nitrogen ranging from 2.6 to 7.4, phosphoric 

 acid from 3. to 10.3, and potash from 4.9 to 14.8 per cent. The 

 hiohest per cents, in the Corn and Potato Manm-es respectively, 

 are but slightly diiFerent, and the same is true of the lowest per 

 cents. 



Bo?fE Manures. 



3Iethod of Yaluation. 



The method adopted for the valuation of bone manures has 

 been already outlined on page 20. Further details are here given, 

 in part reproduced from former Reports. 



Experience has led us to distinguish, for the purpose of valua- 

 tion, five gi-ades of ground bone, the proportions of which are 

 found by a mechanical analysis, i. e., by passing a weighed sample 

 of the bone through a system of four sieves. These five grades 

 have the dimensions, and during 1881, have had the trade-values 

 below specified, viz 



The chemical and mechanical analysis of a sample of ground 

 bone being before us, we separately compute the nitrogen value 

 of each grade of bone which the sample contains, by multiplying 

 the pounds of nitrogen per ton in the sample by the per cent, of 

 each grade, talcing y^th of that product, multiplying it by the 

 eslimated value per pound of nitrogen in that grade, and taking 

 this final product as the result in cents. Summing up the separate 

 values of each grade, thus obtained, together with the values of 

 each grade for phosphoric acid, similarly computed, the total is 

 the estimated value of the sample of bone. 



The following may serve as an example of the valuation of a 



"bone manure by this method, G. W. Miller's Pure Ground Bone, 



632, contained phosphoric acid 23.21 per cent, or 464.2 pounds 



per ton, and nitrogen 3.95 per cent, or 79 pounds per ton. By 



the mechanical analysis it showed : 



42 per cent. fine. 



33 " fine medium. 



22 " medium. 



3 " coarse medium. 



" coarse. 



