A thick cloud of black smoke produced by an airplane flying along the Charles River will announce today the arrival of Major General Amos A. Fries, who will speak at a Union luncheon tomorrow on the subject of chemical warfare. General Fries is chief of the Chemical Warfare Service of the United States Army.

The demonstration which will take place about 12.30, weather permitting, is calculated to emphasize the importance of chemicals in future conflicts. Under cover of such a smoke curtain as will be produced, enemy aircraft could come up to their objective without discovery. The smoke-screen will be produced by ejecting half a ton of smoke-producing liquid from an airplane of special construction, which will be flown from Aberdeen, Maryland, for the purpose.