CHEMISTRY. 



101 



cation afterward of a heat of 100 and up- 

 ward, three hundred and thirty-three volumes 

 of gas were evolved from the metal. 



It appears that when hydrogen is absorbed 

 by palladium the volatility of the gas may be 

 entirely suppressed ; and hydrogen may be 

 largely present in metals without exhibiting 

 any sensible tension at low temperatures. Oc- 

 cluded hydrogen is certainly no longer a gas, 

 whatever may be thought of its physical con- 

 dition. The same conclusion was indicated by 

 another series of experiments, in which it was 

 found that, to be occluded by palladium, and 

 even by iron, hydrogen does not require to be 

 applied under much pressure, but, on the con- 

 trary, when highly rarefied is still freely ab- 

 sorbed by these metals. 



Platinum may be charged with hydrogen 

 by voltaic action, as well as palladium, but 

 with the usual inferior proportion of gas. The 

 charge of hydrogen taken up in a decomposing 

 voltaic cell by old platinum in the form of a 

 tube, of the thickness of a small crucible, was 

 2.19 volumes. This absorbed gas was also readily 

 withdrawn from the platinum and oxidized on 

 reversing the place of the metal in the decom- 

 posing cell. The platinum acquired its well- 

 known polarizing power in virtue of the oc- 

 cluded hydrogen. This power was retained by 

 the metal after being washed with pure water 

 and wiped with a cloth, and was brought into 

 action on placing the metal in dilute acid. The 

 temperature required to expel the hydrogen so 

 absorbed by platinum was found to be little 

 short of a red heat, although the gas had en- 

 tered the metal at a low temperature. 



Soft iron, left some time in a dilute acid, 

 occluded 0.57 volume of hydrogen. This 

 charge of gas was also retained at low tem- 

 peratures, and did not escape into a vacuum 

 till the 'temperature was raised nearly to red- 

 ness. This proves that, like platinum, iron is 

 not penetrated through in the cold by hydro- 

 gen, the temperature of emission being elevated 

 considerably. 



While hydrogen was absorbed freely by 

 palladium and platinum as negative plates, no 

 oxygen whatever was absorbed by plates of 

 the same metals in the position of positive 

 electrodes. Oxygen gas was disengaged freely 

 on the surface of the latter without being con- 

 densed. A platinum plate, which had acted 

 for several hours as a positive electrode, gave 

 afterward, when submitted to heat with ex- 

 haustion, a small trace of carbonic acid but no 

 oxygen. 



The author is inclined to conclude that the 

 passage of hydrogen through a plate of metal 

 is always preceded by the condensation or oc- 

 clusion of the gas. But it must be admitted 

 that^the rapidity of penetration is not in pro- 

 portion to the volume of gas occluded ; other- 

 wise palladium would be much more perme- 

 able at a low than at a high temperature. A 

 plate of that metal was sensibly exhausted of 

 hydrogen gas at 267, but continued permeable, 



and in fact increased greatly in permeability at 

 still higher temperatures, and without becom- 

 ing permeable to other gases at the same time. 

 In a striking experiment, a mixture of equal 

 volumes of hydrogen and carbonic acid was 

 carried through a small palladium tube, of 

 which the internal diameter was three milli- 

 metres, and the thickness of the wall 0.3 milli- 

 metre. From the outer surface of this tube 

 gas escaped into a vacuum, at a red heat, with 

 the enormous velocity of 1017.54 cubic centi- 

 metres per minute for a square metre of sur- 

 face. This gas did not disturb baryta-water. 

 It was pure hydrogen. 



The quantity of hydrogen held by the metal 

 at these high temperatures may become too 

 small to be appreciated ; but Mr. Graham pre- 

 sumes it is still present, and travels through 

 the metal by a kind of rapid cementation. 

 This extreme mobility is a singular property 

 of hydrogen, which was involved in the fun- 

 damental discovery, by MM. II. Sainte-Claire 

 Deville and Troost, of the passage of that gas 

 through plates of iron and platinum at high 

 temperatures. 



Liquid diffusion has also a bearing upon the 

 rapid dissemination of hydrogen through a soft 

 colloid metal, like palladium or platinum, at a 

 high temperature. The liquid diffusion of 

 salts in water is known to be six times as rapid 

 at 100 as at 0. If the diffusion of liquid hy- 

 drogen increases with temperature in an equal 

 ratio, it must become a very rapid movement 

 at a red heat. Although the quantity absorbed 

 may be reduced (or the channel narrowed), 

 the flow of liquid may thus be increased in 

 velocity. The whole phenomena appear to be 

 consistent with the solution of liquid hydrogen 

 in the colloid metal. The " solution affinity " 

 of metals appears to be nearly confined to hy- 

 drogen and carbonic oxide, so that metals are 

 not sensibly penetrated by other gases than 

 these. 



The Velocity of Chemical CJianges. Mr. A. 

 Yernon Harcourt, Secretary of the Chemical 

 Society, associated with Mr. Esson, arrives at 

 the following conclusions after an investigation 

 of the rates at which chemical action takes 

 place : 



1. The rate at which a chemical change proceeds 

 is constant under constant conditions, and is inde- 

 pendent of the time that has elapsed since the change 

 commenced. 



2. "When any substance is undergoing a chemical 

 change, of which no condition varies, excepting the 

 diminution of the changing substance, the amount of 

 change occurring at any moment is directly propor- 

 tional to the quantity of the substance. 



3. When two or more substances act upon one an- 

 other, the amount of action at any moment is directly 

 proportional to the quantity of each of the substances. 



4. When the rate of any chemical change is af- 

 fected by the presence of a substance which itself 

 takes no part in the change, the acceleration or re- 

 tardation produced is directly proportional to the 

 quantity of the substance. 



5. The relation between the rate of a chemical 

 change occurring in a solution and the temperature 

 of the solution is such, that, for every additional de- 



