the facepiece breaks and air is felt to stream into the mask the fit jp defective.

The only conclusive test of the fit of a gas mask is to test it in a gas atmosphere. This test is best carried out in a gas chambcr.

The gas chamber is any room or other enclosed space in which a ga* concentration may be set up and maintained by introducing a chemical agent readily detected at low concentrations (lacrimators arc most frequently used). After fitting with masks and testing them by the

Fig. 122.—To sHur the musk. (1) Position at the eoniniaud "¡slinK." (2> Pn.^iiiR the shoulder HliriK ln«hil»«l the hend nnd over th<- riirht fhoulder :it the " Mn*h-Ct> FftKteiiin* the hook and clasp together.

suction test deserils'd above, the masked men are marched into the g:i> chamber in small groups of from leu to twenty and remain in the gas concentration for a few minutes. If the faccpiece does not fit correctly, or is adjusted iinproj>crly, warning is given in the gas chamber without any more serious effect than a momentary irritation.

Gas-mask Dm ill (17)

Preliminary drill is conducted 14by the numbers" in order to develop proficiency in proper adjustment of (lie mask. Proficiency in this drill is then followed by practice without the numbers to insure as quick an adjustment as possible, and also to give practice in holding the breath. As a rule, careful adjustment is more essential than great speed.

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