Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/565

552 The impurity was called 0 when the impurity was less than .1 = about $1⁄140$ of a cubic centimetre, or = $1⁄100,000$ of the volume of the gases used.

The gases were measured moist, and the surface of the measuring vessel was kept thoroughly moist by washing the apparatus with distilled water in the evening and expelling the water, and then leaving it full of mercury and expelling what had risen through the night, so that no appreciable error was introduced from water present as such in the vessel. One advantage of working with moist gases and vessels with moist surfaces is that the gases can be so completely got rid of, none remaining as a film. When both manometer and measuring vessel were completely filled with mercury and the reservoir lowered so as to produce a Torricellian vacuum in both, it was usual for the mercury to remain for some time 300 to 400 millims. higher in the measuring vessel than in the manometer, the mercury not leaving the moist glass till a trace of gas from the stopcock 2 set it off.

The following experiments taken at random show the modes of measurement and calculation adopted.

Oxygen from mercuric oxide—

Hydrogen from electrolysis of dilute hydrochloric acid—