[29] Part of this section is quoted from “Armies of Industry,” by Crowell and Wilson, Yale Univ. Press.
[30] Which, however, was never used on the battlefield.
[31] See Fieldner and others, J. Ind. Eng. Chem., 11, 519 (1919).
[32] Taken from Fieldner’s article mentioned above.
[33] While it is a well known fact that black smoke is not as efficient as white smoke for screening purposes, the reason for this fact is not clear.
[34] This ultra-microscope is described in J. Am. Chem. Soc. 41, 312 (1919).
[35] Maximum concentration obtainable.
[36] Maximum concentration obtainable.
[37] Maximum concentration obtainable.
[38] Maximum concentration obtainable.