4 
PROF. O. W. RICHARDSON ON THE EMISSION OF ELECTRONS 
of COCl 2 by Kahlbaum. This seems to have the same properties as that which was 
prepared in the laboratory. The chlorine used was prepared by the action of hydro¬ 
chloric acid on manganese dioxide, washed through sulphuric acid and condensed by 
liquid air. As a source of HC1 gas strong hydrochloric acid was taken and the pressure 
reduced by cooling it to a low temperature. For H,0, either water was taken and the 
vapour pressure reduced by mixing it with an excess of sulphuric acid, or crystals of 
CaCL 6H 2 0 cooled below the room temperature were used. 
The electrical arrangements were for the most part of an ordinary character and 
do not call for detailed description. The currents were measured by a quadrant electro¬ 
meter having, except when otherwise stated, a sensitiveness of 570 divisions per volt. 
It is necessary that this instrument should be sensitive, as, although the currents dealt 
with are of considerable magnitude, the differences of potential to be investigated are 
small. One quadrant was connected to the point H in fig. 1, and the other to earth. In 
most of the experiments capacities varying from 0 -01 to 1 mfd. were added to the earthed 
quadrant to reduce the deflections to convenient proportions. Potentials varying 
continuously by any desired amount between ± 20 volts could be applied to the drop, 
by means of a sliding contact on a rheostat fed by a battery with one end earthed, 
and were read by a double-scale Weston Voltmeter. 
In some of the preliminary experiments the alloy was forced through the nozzle in a 
fine stream by admitting inert gas to a pressure of several atmospheres to the space 
above the main body of the alloy in the reservoir. This method was found to be unsatis¬ 
factory, as the stream was apt to get diverted on to the copper ball, owing to some minute 
particle of solid getting into the nozzle or to some slight deposit forming unsymmetri- 
cally at its edge. In the experiments for which data are given the driving pressure 
was only the atmospheric pressure, and the alloy flowed in a steady succession of uniform 
spherical drops. These were about 2 mm. in diameter and flowed at the rate of about 
6 drops a minute in the experiments on which reliance is placed. Different nozzles 
have been tried and other conditions varied, so that experiments have been made 
with drops from about 1 mm. to 1 cm. in diameter and flowing at rates between about 
1 per minute and 15 per minute. So far as I have been able to ascertain, the effects 
recorded are not influenced appreciably by the size and rate of the drops. The size 
(about 3 mm. diameter) and the rate (about 6 per minute) chiefly aimed at Avere 
chosen as being convenient to work with and easy to attain. It should be 
mentioned that with very slow drops irregular results may be obtained, as the 
emission is greatest when each drop starts, and falls off as the surface becomes 
protected by a layer of the reaction products. This effect is always present, but it 
does not appear to lead to serious trouble if the number of drops is not under four 
per minute. 
With the viscous alloys containing a high percentage of sodium, exceptionally large 
and slow drops can be obtained. Some of these formed so slowly that they became 
covered with a visible white coating of the reaction products. As the drop increased in 
