FAMILIAR LETTERS ON CHEMISTRY. 



gas to the extent of many times its volume, ten, twenty, or even, as in the case 

 of ammoniacal gas or muriatic acid gas, eighty or ninety fold which had been 

 long known, no longer remained a mystery. Some gases are absorbed and con- 

 densed within the pores of the charcoal, into a space several hundred times smaller 

 than they before occupied ; and there is now no doubt they there become fluid, or 

 assume a solid state. As in a thousand other instances, chemical action here sup- 

 plants mechanical forces. Adhesion or heterogeneous attraction, as it is termed, ac- 

 quired by this discovery a more extended meaning; it had never before been 

 thought of as a cause of change of state in matter ; but it is now evident that a gas 

 adheres to the surface of a solid body by the same force which condenses it into a 

 liquid. 



The smallest amount of a gas atmospheric air for instance can be compressed 

 into a space a thousand times smaller by mere mechanical pressure, and then its 

 bulk must be to the least measurable surface of a solid body, as a grain of sand 

 to a mountain. By the mere effect of mass the force of gravity gaseous mole- 

 cules are attracted by solids and adhere to their surfaces ; and when to this physical 

 force is added the feeblest chemical affinity, the liquefiable gases cannot retain their 

 gaseous state. The amount of air condensed by these forces upon a square inch 

 of surface is certainly not measurable ; but when a solid body, presenting several 

 hundred square feet of surface within the space of a cubic inch, is brought into 

 a limited volume of gas, we may understand why that volume is diminished, 

 why all gases without exception are absorbed. A cubic inch of charcoal must 

 have, at the lowest computation, a surface of one hundred square feet. This 

 property of absorbing, gases varies with different kinds of charcoal: it is pos- 

 sessed in a higher degree by those containing the most pores, that is, where the 

 pores are finer ; and in a lower degree in the more spongy kinds, that is, where 

 the pores are larger. 



In this manner every porous body rocks, stones, the clods of the fields, &c. im- 

 bibe air, and therefore oxygen ; the smallest solid molecule is thus surrounded by 

 its own atmosphere of condensed oxygen ; and if in their vicinity other bodies 

 exist which have an affinity for oxygen, a combination is effected. When, for in- 

 stance, carbon and hydrogen are thus present, they are converted into nourishment 

 for vegetables into carbonic acid and water. The development of heat when 

 air is imbibed, and the production of steam when the earth is moistened by 

 rain, are acknowledged to be consequences of this condensation by the action of 

 surfaces. 



But the most remarkable and interesting case of this kind of action is the imbi- 

 bition of oxygen by metallic platinum. This metal, when massive, is of a lus- 

 trous white color, but it may be brought, by separating it from its solutions, into 

 so finely divided a state, that its particles no longer reflect light, and it forms a 

 powder as black as soot. In this condition it absorbs eight hundred times its 

 volume of oxygen gas, and this oxygen must be contained within it in a state of 

 condensation very like that of fluid water. 



When gases are thus condensed, that is, their particles made to approximate in 

 this extraordinary manner, their properties can be palpably shown. Their chemical 

 actions become apparent as their physical characteristic disappears. The latter 

 consists in the continual tendency of their particles to separate from each other ; 

 and it is easy to imagine that this elasticity of gaseous bodies is the principal 

 impediment to the operation of their chemical force ; for this becomes more ener- 

 getic as their particles approximate. In that state in which they exist within 

 the pores or upon the surface of solid bodies, their repulsion ceases, and their 

 whole chemical action is exerted. Thus combinations which oxygen cannot enter 

 into, decompositions which it cannot effect while in the state of gas, take place 

 with the greatest facility in the pores of platinum containing condensed oxygen. 

 When a jet of hydrogen gas, for instance, is thrown upon spungy platinum, it com- 

 bines with the oxygen condensed v in the interior of the mass ; at their point of 

 contact water is formed, and as the immediate consequence heat is evolved ; the 

 platinum becomes red hot and the gas is inflamed. If we interrupt the current of 

 the gas, the pores of the platinum become instantaneously filled again with 

 oxygen ; and the same phenomena can be repeated a second time, and so on 

 interminably. 



In finely pulverized platinum, and even in spongy platinum, we therefore pos- 

 sess a perpetuum mobile a mechanism like a watch which runs out and winds 

 itself up a force which is never exhausted competent to produce effects of the 

 most powerful kind, and self-renewed ad infinitum. 



Many phenomena, formerly inexplicable, are satifactorily explained by these re- 

 cently discovered properties of porous bodies. The metamorphosis of alcohol into 



