No. 4.] CHEMICAL AND FARM MANURES. 141 



crop-producing ability of the .same amount of nitrate ni- 

 trogen at 100. At the best, however, no form of organic 

 nitrogen is equal in assimilability to nitrate nitrogen, even 

 dried blood standing at from 76 to 90, as determined by 

 various experimenters, in comparison with nitrate nitrogen 

 at 100. Under the most favorable circumstances, then, it 

 will be seen that in the financial comparison made above 

 the bone was valued too high. It seems probable then from 

 what has preceded that, at $10 per ton for floats and $23 

 per ton for bone of the assumed composition, in a series of 

 years the use of the floats supplemented by nitrate of soda 

 would often prove more generally economical than the bone. 



Basic slag contains from 17 to 20 per cent of phosphoric 

 acid. It is obtained as a by-product in the manufacture of 

 steel from phosphate of iron. Instead of one equivalent of 

 phosphoric acid being combined with three of lime, as in 

 bone, it is in combination in the slag meal with four equiv- 

 alents of lime. In this form, when finely ground, the 

 phosphoric acid is generally considered to be more assimi- 

 lable than that of floats or bone, approaching more closely 

 that of superphosphate. Upon gravelly or sandy soils it 

 would be expected to give even better results than super- 

 phosphates. Wherever the soil is acid it acts exceptionally 

 well, because of its containing one-fourth more lime in com- 

 bination with the phosphoric acid than is the case with bone 

 and floats ; and, furthermore, it contains even a further ex- 

 cess of lime uncombined with phosphoric acid, amounting 

 at present in the best European products to from 8 to 9 per 

 cent. Next to superphosphate, therefore, this can be classed 

 as one of the best forms of phosphoric acid usually ofiered 

 for sale. The price of this product has been not far from 

 $19 per ton, though it should be sold, if manufactured here 

 to any extent, at from $10 to $12. At $19 per ton, one 

 would seldom use basic slag meal as long as acid phosphate 

 is obtainable at from $13 to $14 per ton. 



In the experiments at Kingston, R. I., already referred 

 to, the yields of hay from the use of basic slag upon the uu- 

 limed soil amounted to 13,193 pounds, while with super- 

 phosphates they were as follows : dissolved bone-black, 

 10,017 pounds; dissolved bone, 10,717 pounds; and dis- 



