458 Proceedings of Royal Society of Edinburgh. [sess. 
As a result of several very trustworthy determinations within the 
last decade, the value of J in electrical units for various calories is 
known to at least 1 in 2000. Other electrical methods are that of 
Griffiths already referred to, and that of Ramsay and Marshall 
{Phil. Mag., [5] 41 (1896), pp. 38-52). The method of the latter 
experimenters is a comparative one, benzene being taken as the 
standard substance. Its latent heat was determined by Griffiths- 
and Marshall for this purpose by experiments between 20° and 50% 
extrapolated to the boiling point 80° *2. 
3. No corrections for heat losses are required. 
Preliminary Tests. 
Leakage and Electrolysis . — The copper leads carrying the 
mercury cups pass through wood covered with a layer of water, and 
so are very imperfectly insulated. The method of testing this was 
to raise the electrodes out of the mercury cups, so breaking this 
path. The current which then passed could not he detected by 
the apparatus used. This was with the full battery e.m.f. of over 
4 volts, while the P.D. between these leads during an experiment 
is little over 1 volt. 
That electrolysis does not occur was proved in the first experi- 
ments by severing one of the wires in the heating coil and watch- 
ing for the formation of a bubble or the blackening of the ends as 
the voltage was raised. No appearance of electrolysis was found 
under about 1*7 volts. The above experiment on the leakage 
current applies equally to the inside of the glass vessel, since in 
the early forms of apparatus the copper leads stood in a consider- 
able depth of water, about J inch or so. 
The Temperature of the Boiling Liquid . — This was compared 
with the temperature of the vapour by means of a thermometer 
placed with its bulb first in the liquid and then j ust over the sur- 
face. A difference of -05° was noted. 
Conclusion. 
The experiments made so far have had the end in view of 
testing the reliability of the method, and for this purpose water 
has always been used, in order to enable a comparison to be made 
