Gas density balance employing differential flow measurement

In apparatus for testing gases in which the cooling effect of gases on electrical insistance is measured, a reference gas flows through two conduits 12, 13 containing detectors 14, 15, across which a vertical conduit 16 is connected down stream from the detectors, and provided with a central inlet 17 for the sample gas, the respective outlets being joined to an outlet 20 which is restricted. The reference gas admitted through an inlet 10 is split into two streams flowing in tubes 12, 13, and the sample gas if heavier than the reference gas, tends to flow into the lower tube which thereby slows the flow of that reference gas in the conduit 15, creating an imbalance and the temperature of the resistance rises. The resistances may be replaced by transistors. These are connected in a wheat-stone bridge circuit which may also include a direct recorder. The apparatus is mounted in a chamber maintained at constant temperature, and may be used for testing sample gases from gas chromatography processes.