[95]. Tunneling Machines Successful on Detroit Sewers, Eng. News-Record, Vol. 84, 1920, p. 329.
[96]. Rules on Compressed-Air Work of N. Y. State Industrial Commission, Eng. News-Record, Vol. 85, 1920, p. 1225.
[97]. Taken mainly from the Engineer Field Manual of the U. S. Army; Safety Factors in the Use of Explosives by W. O. Snelling, Technical Paper No. 18, U. S. Bureau of Mines; and an article in Eng’g and Contracting, Vol. 52, 1919, p. 585.
[98]. See paper by C. T. Hall before Am. Inst. Chemical Engineers.
[99]. Per cubic yard of material displaced.
[100]. Eng. News, Vol. 75, 1916, p. 592.
[101]. Pressure of Concrete on Forms Measured in Tests, by E. B. Smith, before Am. Concrete Institute, Feb. 15, 1920. Abstracted in Eng. News-Record, Vol. 84, 1920, p. 665.
[102]. See, also, Concrete Form Design, by E. F. Rockwood, Eng. and Contracting, Vol. 55, 1921, p. 528.
[103]. Includes 6 cents per foot for excavation. Labor for this was 58 per cent of the total labor cost.
[104]. Cement at $1.25 per barrel.