Phenomena of the Capillary Electroscope. 



103 



9. Influence of Chemical Action. 



The movements do not appear to depend upon the chemical nature 

 of the solution, because they take place equally well with acid, 

 alkaline, and neutral liquids. Being also purely physical, they are not 

 dependent upon chemical action ; such action, when it does occur, 

 appears in every case to interfere with them. 



Note.- — Since the publication of a previous communication " On the 

 Capillary Electroscope" (" Proc. Roy. Sob.," vol. 30, p. 32), I 

 have been favoured by M. Lippmann with the following remarks 

 respecting that instrument. "1st. The liquid is to be diluted sul- 

 phuric acid, containing something like one-third its weight of sul- 

 phuric acid. Weak acid does not film glass properly ; most liquids 

 do not; and then stoppages, or a jumping motion of the mercury, 

 occur, such as you have described. 2nd. The capillary tube is to be 

 cut very short (to about 10 millims.) the motions are in that case 

 ten times more rapid than in a tube of 10 centims., because the 

 friction is reduced in that proportion; besides, possibilities for 

 obstruction are reduced also in the same proportion. 3rd. The 

 instrument is only fit for measuring electromotive forces smaller than 

 one Daniell; by using over-great electromotive forces the capillary 

 constant goes over its maximum Value, and then the movement of the 

 mercury is reversed, as you noticed it to be the case at the end of your 

 communication (see, about this maximum, 'Ann. Chimie et Physique,' 

 1875, and also 1877). If you will do me the pleasure of visiting 

 M. Jamin's laboratory in the Sorbonne, you will find there several 

 electrometers in good working order ; three of these are being used 

 by different observers for separate researches, with a precision of 

 _i Daniell." 



