Very respectfully,
F. J. Wilson, Ass’t Engineer.
Erie, May 18th, 1870.
To W. A. Baldwin, Esq.,
Gen’l. Supt. P. and E. Railroad,
Dear Sir: In reply to your inquiry as to the relative difference in dredging rock blasted by Nitro-Glycerin and that blasted by Powder, I have no hesitation in saying that I am certain we can dredge twice the number of cubic yards where it is blasted with the Nitro-Glycerin. I think I could speak safely and say three yards to one where the rock is hard. In fact, there are places where we could do nothing with the Powder blasting, when we have no trouble with the Nitro-Glycerin.
Truly yours,
Chas. F. Dunbar,
Firm of Lee & Dunbar.
Result.—Submarine drilling and blasting with Nitro-Glycerin costs 44½ cents per cubic yard. Gunpowder costs 66¾ cents per cubic yard. Nitro-Glycerin used, one ounce and six-tenths of an ounce per cubic yard of rock removed.