Before finally assembling the apparatus, the various units are charged as follows: A is one-third filled with water to serve as a bubble counter. Generator B is about one-quarter filled with dry arsenious oxide, pea size or powdered. Drying towers G and H are filled with anhydrous calcium chloride. (It is well to place a wad of glass wool in front of the entrance and exit tubes.) In each of the two absorption bottles, J and K, is placed 200 g. (1.25 moles) of ethyl malonate. Dish L is filled with an ice-salt freezing mixture.
 

When assembled as indicated, the apparatus is ready for operation. Concentrated nitric acid is run, in small portions, into generator B from dropping funnel C. After the action has started, the nitric acid must be forced into flask B by applying a small air pressure at the top of dropping funnel C and then opening the stopcock. Later on, when the gas generation slackens, flask B is heated with a smoky flame. The evolution of gas is maintained at a steady rate by increasing the heat until finally all the arsenious oxide has dissolved and the frothing has ceased. During the whole operation a slow stream of compressed air is passed through the apparatus from "bubble counter" A. The stream of air is insufficient if any colorless gas, which turns brown on coming in contact with the air, leaves the apparatus at M. When the arsenious oxide is exhausted, as shown by a slackening in gas evolution, the old generator is removed and a fresh one put in its place. (If the generator is first allowed to cool somewhat, this change can be accomplished without much discomfort.) The moist oxides of nitrogen, in passing up through the condenser D, lose most of their moisture and the gas on passing down through tube E should deposit very little water in trap F. The gas is then thoroughly dried in the towers G and H. When the calcium chloride in G becomes wet (after several runs) the tower is refilled; at the same time G and H are interchanged. After passing through the drying towers and through flask I, the gas is absorbed by the cold ethyl malonate in vessels J and K.
 

(B) Ethyl Oxomalonate.—A rapid stream of nitrous anhydride is passed into the cold ethyl malonate, which becomes dark green in color. There should be an increase in weight of about 200 g. in absorption bottle J in two to three hours.
 

The liquid is left in the freezing mixture for several hours, then gradually allowed to come to room temperature. Red gases are slowly evolved. After standing for two days or more at room temperature, the liquid is transferred to a distilling flask provided with a capillary air intake, and the delivery tube connected with a water-cooled condenser and receiver. The distillation is performed under reduced pressure, by the use of a water pump. Considerable nitric oxide is evolved before the pressure drops to about 70 mm..
 

The first fraction consists mainly of water, a little ethyl acetate, and some ethyl oxomalonate which recombines with the water to form ethyl mesoxalate. When the pressure has dropped to 45 mm. and the temperature has risen to 110°, the receiver is changed. The main product, ethyl oxomalonate, now distils at 110–135°/45–50 mm. If the oxidation has been complete, very little residue is left. Redistillation gives a golden-yellow liquid boiling between 103–108°/15 mm. The yield is 160–165 g. (74–76 per cent of the theoretical amount).