Intelligence and Miscellaneous Articles, 481 



the degree of polish which it has received, is covered with roughnesses 

 forming a sort of network of capillary conduits into which the sur- 

 rounding gases penetrate and condense in quantities which fre- 

 quently are considerable; and the gas-bubbles thus imprisoned become 

 the centres to which pass those which are dissolved. It is observed 

 that effervescence is more brisk the more numerous the roughnesses 

 with which the body is covered. Yet this disengagement is not of 

 indefinite continuance ; for each bubble carries with it a portion of 

 the gas which has produced its formation : the effect first diminishes, 

 and then completely ceases. 



The effect of a prolonged contact is well explained by the slow 

 solution of the condensed gases ; as regards heat, it expels them by 

 expansion, and immersion in water completes the removal of the gas. 



This action of free gases on those in solution accounts for a certain 

 number of phenomena. It explains why a current of air rapidly 

 carries away from a solution all the gas it contains, how also a ga- 

 seous solution exposed to the air gradually becomes impoverished, &c. 



May we not attach to these phenomena the remarkable decompo- 

 sitions of unstable bodies which Thdnard has observed, and studied 

 so completely ? The experiments I have made on acid solutions of 

 oxygenated water appear to confirm this view. 



I. This solution loses oxygen in contact with the air or with 

 gases. When it is shaken with air in closed tubes, there is at once 

 produced an abundant disengagement of oxygen. As in the case of 

 supersaturated solutions, this gas adheres to the air introduced into 

 the liquid. 



II. Solids which under ordinary circumstances decompose it 

 without themselves undergoing any change lose this property when 

 they have been deprived of air by the methods above described. The 

 experiment is very striking with platinum wires, which generally 

 cause an abundant disengagement of gas ; whereas not a single 

 bubble is seen on their surface when they have been heated and then 

 plunged into water for some time. The same effect is obtained with 

 spongy platinum ; but the capillary cavities it contains retain the 

 interposed gas with more force than platinum wires, and it is more 

 difficult to expel the air. — Comptes Rendus, November 19, 1866. 



INDUCTION EXPERIMENTS. BY M. L. DANIEL. 



I replace the moveable armatures of Faraday's electromagnet by 

 two thick plates of soft iron, which are vertical and so high that 

 their ends, which are in the same horizontal plane, just project 

 beyond the two coils. On these two plates, adjusted at a suitable 

 distance apart, I place a third, of the same thickness as the first, and 

 fixed at the end of an iron bar a metre in length. Through the 

 electromagnet I pass the current of [a. battery of four Bunsen's ele- 

 ments. In the circuit a platinum wire is interposed, the length of 

 which is so arranged that it is raised to dull redness. Notwithstand- 

 ing this resistance the contact is strongly attracted. If the contact 

 be separated by pressing with sufficient force at the end of the lever 



Phil. Mag. S. 4. Vol. 33. No. 225. June 1867. 2 I 



