i8o Mr. Herschel on certain motions produced in 
be regarded as merely passive, so far at least as mechanical 
action is concerned. 
28. Potassium. A contact of a single second’s continuance 
with the negative pole of a pile of eight pairs, in feeble action 
under liquid potash, imparted to 100 grains of mercury the 
property of rotating violently from the positive to the ne- 
gative pole, the circuit being completed in the liquid alone. 
The rotation was forcible when this alloy was diluted with 
100 grains more of pure mercury, and was still sensible after 
the addition of another equal quantity. In this latter case, the 
quantity of potassium present could hardly be estimated at a 
millionth part of the whole mass. 
39. Sodium. Under a solution of soda I electrised 100 grains 
of mercury during 80 seconds with the above mentioned Vol- 
taic power, the mercury being in contact with the negative 
wire. It was then washed hastily, and introduced under a glass 
bell into dilute muriatic acid, which disengaged 95 mercury 
grain measures of pure hydrogen. Consequently, it contained 
less than ~ of a grain of sodium ; and as in such extremely 
small quantities the production of the alloying metal must go 
on uniformly, a contact of 1" would have produced only ~ of 
the quantity, or -^doo °f a g ra i n ; that is of the whole 
mass. This being premised, a contact of 1 second in dura- 
tion was made under similar circumstances, with 100 grains 
of fresh mercury, which was thus found to have acquired a 
powerful rotatory property. This was now diluted with 100 
grains more of the pure metal, in which, therefore, the sodium 
was only in the proportion of 1 to 800,000. The rotation was 
enfeebled, but was still full and distinct. Being again diluted 
with 100 grains more of mercury, so as to make the propor- 
