Lachrymators
While one cannot determine the lethal concentrations of poison gases for men, it is possible to determine the concentration that will produce lachrymation. The threshold value is that at which two-thirds of the observers experience irritation. The lachrymatory value is considerably higher than the threshold value.
Fig. 117.—Aeration Apparatus for Testing Lachrymators.
A very satisfactory method for determining lachrymatory values is shown in [Fig. 117]. Air is measured at A and bubbled through the lachrymatory substance in B. The air and gas are mixed in D and pass into E, a gas-tight, glass-walled chamber of about 150 liters capacity. The gas is removed through Ef, by suction and the volume of the air-gas mixture measured by the flow meter, F.
After the apparatus has run a few minutes, and the concentration of the gas has become constant, the subject is instructed to adjust the mask, attached at H, and to tell whatever he notices just as soon as he notices it. The operator stands in such a position that he can manipulate the stopcock H without being observed by the subject. After breathing air for a time (H is a two-way cock, connected with the air through J, and to the chamber through Eg) both to become accustomed to the mask and to eliminate, as far as possible, any “psychological symptoms,” the subject is allowed to breathe the gas mixture for a maximum of three minutes. If the expected symptoms are produced in less than this time, the test is discontinued as soon as they develop.
Fig. 118.—Type of Spray Nozzles.
For accurate work, it is necessary to work with a pure sample which is at least fairly volatile. Mixtures cannot be run by this method. In this case it is necessary to volatilize each separately, passing the vapors simultaneously into the mixing chamber E.
A spray method may also be used with satisfactory results. Types of sprays are shown in [Fig. 118].