M. Becquerel on Chemico -capillary Actions. 439 



metallic reductions which he has described. Before examining 

 the explanations he has given and the experimental proofs on 

 which he rests them, it will be convenient to dwell on some facts 

 of detail which he developes in various parts of his investi- 

 gation. 



Among these may first be noticed the effects produced by dif- 

 ferent kinds of diaphragms, such as bruised quartz and glass in 

 thin layers, fine sand, and hardened mortar, the interstices of 

 which are capillary spaces. To examine the effect of fine sand, 

 he introduces a certain quantity into tubes closed with a piece of 

 sackcloth bound by means of a wire on the outside, thus forming 

 diaphragms of 4 to 5 centims. in height ; he then places suc- 

 cessively various metallic solutions in the tube, and the solution 

 of monosulphide of sodium in the test-glass, taking care that the 

 sand is fine enough and the height of the column sufficient to 

 allow the liquids only to mix slowly. Most metals are thus re- 

 duced from their solutions ; it is thus with copper, silver, gold, 

 cobalt, nickel, &c. A solution of equal parts of nitrate of cop- 

 per and of silver first gives the silver in dendrites or in plates ; 

 then comes the copper, but after a considerable interval. With 

 hardened mortar the reduction of platinum, cobalt, &c. is effected. 

 M. Becquerel has also endeavoured to replace, in his old experi- 

 ments on simple electrochemical apparatus, the kaolin which he 

 used as a diaphragm by cracks in tubes. Thus in the couple 

 which is called the oxygen one, he substituted for the tube filled 

 with kaolin, which separated the solution of caustic potash from 

 nitric acid, a slit tube closed by the lamp at one end, and he ob- 

 tained the same effects. The same result was obtained in other 

 analogous cases, in which he used simple electrochemical appa- 

 ratus for obtaining simple and double sulphides and iodides. 



M. Becquerel thinks the reduction of metals in capillary spaces 

 cannot be explained, as has been attempted, simply by reference 

 to molecular attraction, but that it is due to the combined actions 

 of affinity, molecular attraction, and electricity. 



In order to show the influence of electricity in the production 

 of the phenomenon, M. Becquerel uses the apparatus consisting 

 of a cracked glass tube filled with a solution of nitrate of copper, 

 which is immersed in a test-glass containing a solution of mono- 

 sulphide of sodium ; he then connects these two solutions by a 

 platinum or copper wire, which by completing the circuit forms 

 a simple electrochemical couple, which gives rise to a current 

 which is indicated by the galvanometer. In a short time the 

 solution of nitrate of copper is decomposed, and the end of the 

 wire which is immersed in this solution is covered with metallic 

 copper. During these reactions the crack only acts by making 

 contact between the two solutions; no trace of metallic copper 



