Quantitative Relationships

It has been found that, if the optical readings from the Tyndall meter are plotted as ordinates against the time t (the time elapsed after detonation) as abcissas, and that portion of the curve between t = 0 and t = 30 considered, the curve generally descends sharply at first, from a high point representing the density immediately after the production of the smoke, to a point in the neighborhood of t = 8, where it flattens out and descends much more slowly with a slope that changes little. The area under the significant portion of the curve, that is, the area circumscribed by the curve from the point t₃₀ to t₀, the vertical axis from this point to the origin, the horizontal axis from the origin to t₃₀ and the line perpendicular to this axis, cutting the curve at t₃₀, is a rough measure of the relative values of different smokes. This area is calculated as the sum of two rectangles, from t₀ to t₈ and from t₈ to t₃₀.

Some results are as follows:

Area 30
Phenyldichloroarsine181
Triphenyldichloroarsine  178
Diphenylcyanoarsine137
Diphenylchloroarsine101
Cyanogen bromide 94
Methyl dichloroarsine 70
Phenylimidophosgene 69
Mustard gas 38

The curves in [Fig. 101] show the way in which the readings fall off with time. Each substance of course has its characteristic curves.

Fig. 101.—Typical Curves Showing the Decrease
in Concentration of Smoke Cloud with Time.