the repulsive energy of molecules at the greater distances, as given in Table I (p. 68); if we regard the coefficient, m, as constant, whatever may be the value of r. In fact the value of m, depends upon the pressure to which the molecular atmospheres are exposed (p. 241, foot note); and this, in gases, must depend mainly upon the barometric pressure, and be constant for the same pressure. It is to be observed that the results given in Table I hold good for compound molecules, provided as they are with their own especial atmospheres (p. 241), as well as for simple molecules. If r, the radius of the atmosphere of the molecule, be increased in any ratio, the value of (=) will be diminished m)

in proportion to the square of this ratio, but if we estimate the force at a given distance, this distance, as expressed in terms of r, will be diminished in the same ratio that r is increased, and hence if the force varies inversely as the square of the distance, its value at the given distance will be the same as before. The elastic force of molecules posited at the same distance from each other should therefore be the same, whatever may be the radius, r, of the molecule, simple or compound. This result depends upon the assumption that the force of molecular repulsion varies, beyond a certain limit, inversely as the square of the distance. Table I shows that for the smaller values of the ratio, (which should

n

m

be taken for liquids that furnish vapors, and substances that habitually exist in the gaseous form), we have nearly reached this limit at the distance 80r.

n

m

n

m

To this it should be added that the calculations are made upon the supposition that the ratio remains constant for each set of computations, answering to each special value of 2. But as a matter of fact, in the transition from the liquid to the vaporous state, as we have seen (p. 75), the molecular atmospheres expand, which should diminish the value of n, and of the ratio 22. Accordingly, to represent truly the vaporous state, it is probable that the calculations should be made for a smaller value of

m

n

m

than any of those given at the head of the Table. If this be true the limit above referred to may be greatly reduced. This should be the case especially with the permanent gases. The distinction between the gases and vapors lies, in all probability, in the fact of a smaller value of " for the former than the lat

n

m

ter; in consequence of which compression, or reduction of tem

perature of the permanent gases does not increase this value to the limit 4.93 at which the liquid state becomes possible.

The received theory among chemists, of combination by volume is in entire accordance with these results derived from our theory of molecular forces, and with the conception to which we have been led, of the constitution of simple, and compound molecules (p. 239, &c.). If we suppose, with the chemists, that in general the ultimate molecule is composed of two "atoms," this is equivalent to saying, in the language of the present theory, that the ultimate molecule is a compound molecule consisting of two simple molecules united together, and provided with its own proper atmosphere.

บ

All such binary molecules of elementary gases will occupy, as we have seen, the same space, which may be called the unit of volume. If v represent any given volume, as a cubic inch, and n the number of atoms in v, then this unit of volume will be. Now if one volume of one gas be presented to one volume of another the general result is that two volumes of a compound gas are formed. This implies that each of the binary molecules is decomposed, each atom of the one combines with one of the other, and thus two new compound molecules are formed, each occupying one unit of volume. If, as in the formation of carbonic acid, one volume of one gas unites with one volume of another, and one volume of compound gas is formed, we must suppose that the two binary molecules unite, as wholes, and form one new molecule containing four atoms associated in pairs. Again, if, as in the formation of aqueous vapor, two volumes of one gas combine with one of the other, and two volumes are formed, we now have two molecules a and b combining with one, c; c must be decomposed, and one of its atoms must combine with a, and another with b. Thus each molecule of water contains two atoms of hydrogen, associated with one atom of oxygen. If, as in the production of ammonia, three volumes unite with one, and two volumes are produced, three molecules must combine with one and two new compound molecules result. This implies that the single molecule and one of the three molecules are decomposed, and that the disunited atoms combine with the other two. If the molecules of the two gases, or vapors, that combine, be ever so complex, and the same number of volumes unite as we have above supposed, with the same result as to the number of volumes produced, the processes will be essentially the same as just indicated. Each compound molecule will occupy one unit of volume, whatever number of atoms, or groups of atoms, it may contain.

The decomposition of molecules which occurs in such cases, must be attributed to the molecular polarization that precedes and

accompanies the act of combination; in conjunction with, under special circumstances, the exertion of a separating force due to heat, light, or an electric current. We have seen already, in considering the process of decomposition of a molecule of water by the chemical action of zinc (p. 251), that such action upon one of the elements of a binary compound tends to separate it from the other, if the two are in conducting communication; as they would be in every true compound molecule, by reason of the electric ether condensed between them.

Chemical action of the Actinic rays.-We understand by the actinic rays, the solar rays of high refrangibility, which are capable of producing chemical effects entirely distinct from the effects of heat. From the view we have taken of the origin of rays of heat and light (p. 217, &c.), we are led to conceive of all the solar radiations as essentially of the same nature, and differing only in the rapidity of vibration, and in the intensity of the impulses propagated in the ray; and that they owe these differences to the fact that they originate in the vibrations of the atomettes of molecular atmospheres, posited at various distances from the central atoms of the molecules (p. 217). The most refrangible actinic rays should then emanate from the atomettes that lie at the greatest distances from these atoms.

The chemical action of light, and of the actinic rays in general, appears to be a consequence of the feeble repulsive individual impulses propagated in the rays that originate in the upper portions of molecular atmospheres. Such feeble impulses cannot penetrate far into the molecular atmospheres upon which they fall, and must pass around them. They should accordingly tend to urge a portion of the electric ether that may lie in their route around to the farther side of the molecule, and so to bring it into a state of positive electrization. The nature of the action that will ensue, in consequence, upon the next molecule beyond that which receives the ray, must depend upon whether there is an electric conducting connection between the two or not. If there be such connection the tendency of the action of the free electricity set in motion will be to separate or decompose the two molecules; which, in the case supposed, will be chemically united. The action here considered is essentially the same as that which occurs in the decomposition of water by zinc (p. 251). Most cases of the chemical action of light would seem to be explicable upon this idea. Thus we may explain the action of light upon an explosive mixture of chlorine and hydrogen, by the decomposition of the elementary molecules of the two gases, and the resulting formation of two molecules of hydrochloric acid. The reduction of the chlorid of silver to a subchlorid by the action of light, might result from the same general tendency to effect a decomposition of united molecules.

Heat may, in some cases, produce the same chemical result as light, or the actinic rays generally. For example, it explodes the mixture of chlorine and hydrogen. But the effect must be ascribed to the repulsive action of the heat-pulses taken up by the molecular atmospheres, at considerable depths below their surface; whereas the separating action of the actinic rays is probably due to a movement of the electric ether effected at the surface of the atmospheres. It is questionable whether the actinic rays are capable of imparting any sensible polarization to molecules. In this respect their tendency is the reverse of that of heat, viz: to impart a negative, instead of a positive polarity. For their impulses act directly upon the ether of the molecular atmospheres, but the heat impulses, as we have seen, act indirectly, producing expansion. The distinction is the same, essentially, as that taken between the two modes of action of the external impulses exerted by electric currents (p. 65); the one, analogous to light, developing magnetic currents in groups of molecules, and the other, like heat, determining a reverse polarization of molecules, compound, or simple, by an indirect expansive action.

New Haven, Jan. 15, 1866.

ART. XXVIII.-Analyses of Rahtite, Marcylite and Moronolite; by Mr. S. W. TYLER, A.B., member of the Mining School of Freiberg, Saxony, with prefatory remarks by Prof. CHARLES U. SHEPARD.

1. Rahtite. This mineral was distinguished by me as a new species in March, 1861, during a survey of the Ducktown copper mines, Tennessee, where it was found in the upper, decomposed portions of the great copper-lodes, associated with melaconite and with various mixtures, of chalcopyrite, redruthite and melaconite, and also more rarely with galena and cuprite.

In structure it is quite massive, though at first inspection it seems highly crystalline; but this deceptive appearance arises from its being traversed in all directions by slender prismatic cavities imparted to it by some unknown mineral which has wholly disappeared. The walls of these cells are polished and bright. The color of the mineral is dark lead-gray with a tinge of blue, not unlike some of the ores of antimony. Its hardness and density are given below by Mr. Tyler. Thus far, it has only been found in small quantities. The name is bestowed in honor of Capt. Raht, himself a student of the Freiberg School, and now for many years the well known manager of the principal Duck

town mines.

The following are Mr. Tyler's description and analysis of the specimen submitted to him by me for examination :

AM. JOUR. SCI.-SECOND SERIES, VOL. XLI, No. 122.-MARCH, 1866.

"The fragments of the mineral which afforded material for the following analysis appeared to be composed of crystals, but so interwoven and indistinct that a determination of their form was impossible.

The mineral possesses a hardness of 3.5; specific gravity, 4.128 (mean of three trials which gave respectively 4.07, 4·126 and 4-188); light reddish-brown streak; metallic luster; and is of an iron-black color.

Before the blowpipe, on charcoal, it melts, with the appearance of effervescence, and coats the charcoal with oxyd of zinc. With carbonate of soda melts to a bead; which, if moistened and brought in contact with silver, blackens the latter, showing sulphur to be present. A coating of oxyd of zinc is also formed upon the coal, and metallic particles remain in the soda, of iron and copper. With microcosmic salt, in the oxydizing flame, after being strongly ignited on charcoal, it gives a bead which is green while hot, but on cooling becomes blue; and which, if treated with tin, in the reducing flame, turns of a dull red. Heated in an open glass tube it gives off sulphurous acid and turns brown. In the closed tube it remains unchanged.

The mineral was dissolved in fuming nitric acid. The sulphur which separated was collected on a dried and weighed filter, dried at 100° C., and weighed with the filter. The sulphur which had been oxydized in the process of solution to sulphuric acid was precipitated with chlorid of barium. After the excess of the latter had been removed by adding sulphuric acid, the copper was precipitated by means of sulphuretted hydrogen, and determined as sulphid of copper (Cu2S) by Rose's method, viz: heating with a little sulphur, to redness, in a current of hydrogen gas. The iron was then precipitated, after neutralization, with acetate of soda as basic acetate of iron, ignited and weighed as oxyd of iron. Sulphid of ammonium was added to precipitate the zinc, which was determined as sulphid (ZnS) in the same manner as the copper.

5935 grm. of the mineral gave 0675 S; 9505 BaOSO3, containing 1305 S; 1041 Cu S, containing 0831 Cu; '0552 Fe1O3, containing 0366 Fe; 4238 ZnS, containing 2840 Zn.

2. Marcylite.-Marcylite is described on page 405 of my Mineralogy; but from less pure specimens than those submitted to Mr. Tyler. Mine appears to have contained an intermixture of