The determination of gaseous densities

The microbalance technique for the determination of gaseous densities is examined and the require­ ments stated for its use as a method of high precision and reliability. A detailed description is given of the construction of a sensitive and stable quartz microbalance and of the precautions necessary to obtain reproducible gas-pressure measurements of high precision. The improved technique is used for the determination of the atomic weights of carbon and nitro­ gen by the comparison of the pressure ratios at * limiting density ’ of the pure gases nitrogen, methane and oxygen; the values obtained are: nitrogen 14.0078 (± 0*0003) carbon 12.0112 (± 0*0005) Nitrogen prepared by heating pure, dry sodium azide is shown to contain traces of hydrogen (either in the free state or combined with nitrogen as ammonia), and a new method is described of purifying nitrogen made by this method.