BULLETIN OF THE BUSSEY INSTITUTION. 187 
Still further evidence, of a kind more conclusive, perhaps, to some 
minds than the foregoing, will be found in the following statement of a 
farmer’s practical experience as to the cost of making superphosphate 
from spent bone-black and oil of vitriol, at a farm about twelve miles 
from Boston. The experience is that of Mr. Henry Saltonstall, 
Treasurer of the Massachusetts Society for Promoting Agriculture ; 
and it is all the more valuable in its bearings upon the present aspect 
of the question of the valuation of soluble phosphoric acid, because 
the information was gained as an incidental result of actual work at 
the farm, that had been performed without the slightest reference to its 
connection with the subject now in question ; in fact, without thought 
of formulating the results, or of paying any heed to them whatsoever. 
Having learned by chance that Mr. Saltonstall had had a quantity 
of superphosphate made at his farm from bone-black, I wrote for a 
fair sample of the product, in order to get an idea of what its quality 
might be. Analysis showed that the sample sent by Mr. Saltonstall 
contained : — 
Pemeineeexoclegabcl2°. . . fw wt Cf «84.108 
Volatile matter (beside moisture) . . . . . 16.70 
OTION.  . ws ww ts es «49.20 
| 100.00 
The specimen contained : — 
Phosphoric acid soluble in water . . . . . 11.24% 
eet 45) Insoluble se Bid sel att) a PLD 
Ree aa igh MIE TSA 14.39% 
The large amount of moisture indicated by the analysis was no less 
surprising than the really excellent quality of this home-made fertil- 
izer. In reply to my inquiries, Mr. Saltonstall wrote as follows :— 
‘¢ My foreman says he dug the sample out of the middle of the pile, and 
that all the dampness or moisture that was ever in it had had no chance 
to dry off. 
‘* To 2100 Ibs. of bone-black he put 1050 Ibs. sulphuric acid, and half 
will deliver in Boston a soluble phosphate of lime of very high grade, — guaran- 
teeing 87% (thirty-seven per cent) of anhydrous phosphoric acid soluble in water, 
—at $90.00 per ton, and pro rata for a higher percentage ; the exceedingly con- 
centrated form of this fertilizer enabling him to bear the cost of its transportation. 
* The sample came to hand in a tightly closed bottle, and was analyzed im- 
mediately with the results given above. Another estimation of the moisture, 
made after the bottle with its contents had stood several weeks in a warm room, 
gave 32.56%. 
