The Davis-Bournonville Company has recently added to its line apparatus for the production of oxygen. The method is similar to the Oxygenite process, but the oxygen mixture is not combustible; it must be heated externally with a gas flame. This mixture is composed of potassium chlorate, 100 parts, and manganese dioxid, 13 parts; both should be fairly pure to insure a gas of 97 to 98 per cent estimated purity after three scrubbings.

Figure 40 shows the apparatus in position. The oxygen mixture is charged into the retort, which should be as full as possible to exclude ordinary air. The retort is heated with a slow gas flame so that the generation is regular; as the heating proceeds the flame is raised to drive off the last of the oxygen. The oxygen generated passes through three washer tanks filled with sodium hydroxid solution, and then into a gasometer. From the gasometer the gas is compressed by a two-stage compressor into pressed-steel cylinders, at a pressure of 300 pounds to the inch. This for the reason that considerable pressure is needed to make a good jet flame, especially in cutting metals.

This method of generating oxygen takes more time than the Oxygenite process; and it necessitates a compressor pump while the latter does not. The advantages claimed for it are: that there is little oxygen lost when the retort is recharged, because the pressure is low in all of the chambers; that loss from leakage is much less; that the bubbles of gas being much more expanded in passing through the hydroxid solution are washed much more thoroughly.

One writer1 estimates the cost of the oxygen mixture, when made from fairly pure chemicals, at eight cents a pound. One pound producing 4 to 4 1/2 feet, brings the cost of the oxygen to about 2.25 cents a cubic foot. This is exclusive of freight and operating charges.