276 Mr. Herschel on certain Motions produced in Fluid [Oct. 



soda, pretty highly impregnated with the caustic alkali, for the 

 conducting liquid. This has the advantages at once of high 

 conducting power, and of producing no currents whatever in 

 pure mercury, neither pole being placed in contact. Of course, 

 whatever motions arise on the introduction of an extraneous 

 metal must be due entirely to the presence of that metal, and 

 the mercury may 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 negative 

 pole, the circuit being completed in the liquid alone. The rota- 

 tion 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. 



29. 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 T ' 7 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 \" would have produced only -^ of the 

 quantity, or T „Vo- °f a grain ; that is - 4 J „ of the whole mass. 

 This being premised, a contact of 1 second in duration was made 

 under similar circumstances with 100 grains of fresh mercury, 

 which was thus found to have acquired a powerful rotatory pro- 

 perty. This was now diluted with 100 grains more of the pure 

 metal, in which, therefore, the sodium was only in the propor- 

 tion 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 proportion of sodium 1 : 1,200,000, 

 there was still a considerable radiation from the positive pole, 

 but not extending over the whole surface. On reducing the 

 proportion of sodium by a third addition of an equal quantity of 

 the pure metal to 1 : 1,600,000, a. feeble radiation was still sen- 

 sible in the same direction. 



30. Ammonium. — A considerable quantity of the amalgam of 

 this singular substance introduced into mercury under a sol u- 

 tion of soda did not communicate to it any power of rotat ion. 

 This remarkable result, which goes to separate ammonium by a 

 definite character from the other metallic bases of the al kalies, 

 was again obtained on repeating the experiment. It is po ssible, 



