Patent GB-459721-A (GB)
Title: Improvements in or relating to pest extermination
IPC: A01M13/00
Filed: 1935-07-10
Abstract: 459,721. Fumigating. DEUTSCHE GES. FUR SCHADLINGS - BEKAMPFUNG, 7, Weissfrauenstrasse, Frankfort - on - Main, Germany. July 10, 1935, Nos. 19765 and 19766. Convention dates, July 25, 1934 and March 6, 1935. [Classes 49, 81 (i), and 130] [See also Group I] Pests are exterminated by circulating air or other gas through a volatile toxic substance and a fumigating chamber containing the material to be treated, e.g. furniture, clothing, cereals, tobacco, or dried fruits, by means of a compression pump, the chamber being under considerably reduced pressure and a constriction being provided in the gas passage between the pump and the point of entry of the gas into the actual fumigating space so that during each cycle the gas is compressed, acts in this state on the toxic substance, and expands before its entry into the fumigating space, the constriction being such that the resulting compression increases the temperature of the gas sufficiently to equalize, entirely or substantially, the fall caused by vaporization of the toxic substance. Air is removed from the fumigating chamber a by a pump c, valve g being closed and valves m and s open. Valves g and k are opened and s closed and the remaining air circulated through the generator e, containing, for example, hydrogen cyanide, ethylene oxide or carbon disulphide, or carriers charged therewith, and the chamber. The throttle valve g is adjusted so that compression of the air gives the desired increase of temperature. Instead of or in addition to a regulatable valve g, a nozzle or other constriction may be provided between the pressure side of the pump and the chamber, for instance, in the pump itself. The air evacuated from the chamber may first be passed through a jacket h of the generator e and throttled by the valve i so that its heat of compression is utilized. Hot exhaust gas of the pump motor, steam or the like may heat the contents of the generator and, charged with toxic gas, may enter the working gas cycle with, or in place of the air. Circulation may be interrupted when the desired concentration of toxic vapour is attained, or the generator cut out of circuit. The generator instead of being in the gas circuit may be connected by a pipe to any point of the gas passage on the pressure side of the pump. The toxic substance or carrier may be introduced into the gas stream prior to the entry of the gas into the actual fumigating space, in such a tightly packed condition that its resistance produces the desired compression and heating of the gas. Thus, it may be packed into the generator, or into the fumigating chamber directly behind the gas inlet. Heating tubes or a double bottom in the chamber may then be provided for circulating hot exhaust gases or steam. Finally, the gas is removed from the chamber and the chamber flushed with air. A little air may be supplied through valve t before evacuating. The removed gas may be led to a reservoir, which may be constituted by the generator, and used again. Two or more chambers may be employed, the residual gas from one being transferred to another, previously evacuated chamber. In an example, pressure in the fumigating chamber is first reduced to 160 mm. and the residual air circulated through hydrocyanic acid absorbed by kieselguhr, the pressure meanwhile being 140 mm. and the excess pressure between the pump and the throttling position being 1 atmosphere. Circulation may be continued with the poison gas generator out of circuit and without throttling. Air may then be admitted to give a pressure in the chamber of about 360 mm. before discharging. Specification 23954/07, [Class 81], is referred to.