403 On definite Proportions. 



inches in diameter, and on it the soUition of potass ; I in- 

 troduced the iron wire of the negalive pole into the quicfe- 

 silver, and brought a spiral wire of platina, which com- 

 municated with the positive pole of the column, into the 

 solution, at the distance of about a line from the surface of 

 the quicksilver: its coils were nearly in one plane, and 

 parallel to the surface of the quicksilver: a plate of platina 

 would have been less fit for the purpose, since its lower 

 surface would have become continuallv covered with bub- 

 bles of oxygen, which could not have escaped. In this 

 apparatus the decomposition of potass took place very ra- 

 pidly; and in 24 hours the quicksilver, which weighed 

 about SO grammes, or 2| ounces troy, was so impregnated 

 with potassium, that it was no longer fluid. It is evident 

 that by a greater number of plates the intensity of the 

 charge might have been so much increased, that this eti- 

 larged surface would still have been too small for the de- 

 composition of the potass only. 



Since in the operation of the column upon a saturated 

 solution of potass, when quicksilver forms the negative 

 conductor, the affinity of potassium for oxygen appears the 

 weaker, it seems to follow that potass alone should be de- 

 composed when the force of the colunm is infinitely small. 

 In order to examine this point, I constructed a column 

 with 20 pairs of zinc and copper plates, l| inch in diame- 

 ter, placing bttween them pieces of cloth moistened with 

 a solution of salt. When I exposed a saturated solutioi^ 

 of caustic potass to the operation of this column, in the 

 apparaius first described, the positive wire emitted oxygen 

 in small quantities, while no extrication of gas was obser- 

 vable at the surface of the quicksilver. At the expiration of 

 six hours, a globule of quicksilver taken out of the apparatus 

 already exhibited evident traces of potassium ; and after 

 24 hours I found the quicksilver strongly impregnated with 

 it, so that it caused an extrication of gas in pure water for 

 several hours. 



What has hitherto been mentioned, relates more to the 

 physical properties of the electrical column than to the 

 decoiuposiiion of the alkalis : it deserved however to be 

 noticed, as a caution to those experimenters, who have the 

 coumnand of a column of large plates, in order that they 

 may be aware of the danger of falling to obtain the greatest 

 possible effect in saturated solutions, like those of the caustic 

 alkalis by employing too small a surface in the immediate 

 operation of decomposition: while in the decomposition of 

 the alkaline earths, as will be seen hereafter, another mode 



of 



