Flit gun

A Flit gun is a hand-pumped insecticide sprayer used to dispense FLIT, a brand-name insecticide widely used against flies and mosquitoes between 1928 and the mid-1950s. Although named after the well-known brand, "Flit gun" became a generic name for this type of dispenser. Once commonly found in households, hand-operated Flit guns have been replaced by aerosol spray cans and fallen out of common use.
Design description.
A Flit gun consists of a pneumatic pump cylinder with a hand-operated piston to force air through an air nozzle in the front. Below the front of the pneumatic tube hangs a cylindrical container which acts as a reservoir for liquid insecticide, this reservoir being set at 90 degrees to the pneumatic tube. In early versions, the reservoir is permanently secured to the pump and equipped with a removable, gasketed screw cap for filling. In later, improved versions, the insecticide reservoir is secured to the pump with a coarse screw fitting and a seal of cork composite or gasket paper, so that it can readily be unscrewed for filling. A siphon tube extends from the pump cylinder downward into the reservoir and the upper end of the siphon is positioned in front of a nozzle on the air pump. When a jet of high-velocity air exits the pump and streams across end of the siphon tube, it lowers the pressure in the siphon (Bernoulli's principle), drawing insecticide upward from the reservoir, which then atomizes the liquid as it is entrained in the air jet (it is an atomizer nozzle). With each vigorous forward stroke of the pump handle a burst of spray is produced, similar to that of a modern aerosol spray can.