Use of Illuminating Gas to Check Metabolism Apparatus

Combustion of alcohol, ether or acetone is standard procedure to check the operation of metabolism apparatus (Carpenter, et al. 1 ). We have found it impossible, however, to devise a burner by which the combustion of any of these would proceed evenly for meta-bolically significant periods at rates comparable to the respiratory metabolism of the rat. On the other hand, small validity would seem to attach to a test several times more severe than planned capacity; failure would be no indication of inability of the apparatus to do what it was designed to do; nor would success be any guarantee that it could perform the more delicate task for which it was made. A micro-balance is not checked with kilogram weights.

As a result, recourse has been had to combustion of gas which can be successfully controlled at almost any desired rate. It was originally intended to use a pure, commercial preparation of one of the lower hydrocarbons in order to eliminate the necessity of control determinations. Preliminary work with ordinary illuminating gas from the city mains was so satisfactory, however, that it has been adhered to; especially since equipment was at hand for the necessary control determinations which involve only slightly additional work.

Since the only difficulty in the application of this principle is accurate measurement of the small volume of gas burned, description of an apparatus which has been found accurate and simple to operate and is easily assembled from odds and ends about any laboratory may be of interest.

This apparatus is shown diagrammatically in Fig. 1.

The gas sample. Since the composition of the city gas supply is not absolutely constant, gas is not burned directly from the supply line. Instead, a sufficient sample for several runs and their attendant control determinations is secured in the 18 liter carboy (C₁) by water displacement into the similar carboy (C).