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And to this was added an equal weight of pure silver powder. The arc spectrum was then photographed under conditions similar to those of the aerolites.

It was seen that the chromium groups were still the most prominent lines in the spectrum, those of nickel being comparatively faint.

Keeping the other ingredients constant and gradually reducing the proportion of chromium several more experi ments were made, and it was found that when the chromium had been so reduced that it was only 0.16 per cent, the lines A 4862'02 and λ 4870 9 were no longer Visible; a further experiment with electrodes containing only o'I per cent chromium distinctly showed the other two groups.

These experiments show that it is easy to detect the presence of chromium in an arc between electrodes that contain only 5 parts Cr in 10,000.

A 3593 633, A 3605 478, and the closely adjacent nickel lines; it was found that when the amount of nickel was reduced to 0'04 per cent the line 3619'391 was only just visible.

The information gained from these mixtures of chromium and of nickel made it possible to obtain an approximate estimate of the quantities of these elements present in the three aerolites, El Nakhla, Aubres, and Bustee. A mixture containing chromium o'25 per cent and nickel 0:04 per cent gave a photograph which for Cr-Ni was practically identical with that of Aubres.

The estimation made in this way cannot be more than a "good approximation" on account of unavoidable variations, due to intensity of light and time of exposure ; also to conditions of photographic development, which cannot be exactly controlled, but the indications given by the relative intensities of closely adjacent Ni and Cr lines when they occur on the same film are very much more exact, and the result proves that in these aerolites the element chromium exists in greater abundance than nickel. To this fact must be added that of the almost total absence of chromium in the familiar nickeliferous irons of the siderites.

In a general survey of the spectrum analyses of the 30 aerolites which forms the subject of this paper, the most striking fact is their similarity in composition, and the small number of elements represented. Making full allowance for wide differences in the photographic activity of the arc spectra of the elements, it is remarkable that we only see with certainty the lines due to some ten bodies, and of these ten, four only-iron, chromium, magnesium, and nickel - appear to be present in quantity. With three exceptions, Bustee, El Nakhla, and Aubres, the proportion between these elements appears to be practically the same in all.

(Without anticipating this communication on siderites, I desire to point out the remarkable fact that although the chromium lines arpear, sometimes very strongly, in all my aerolite spectra they do not appear in any of the siderites I have so far examined-except in one instance, that of "Zacatecas " Although of course the nickel lines are always visible-from the spectroscopic examination of a number of specimens of iron, to which I had added decreasing amounts of chromium, I found that the dominant lines of chromium were quite visible even when the amount present was no more than o'0175 per cent. This is due to the fact that chromium is absent from the nickelirons but almost universally present in the aerolites in the form of chromite. In Aubres, &c., there is probably more chromite than nickel-iron. In the magma which produced meteorites all the Cr was converted into oxide or sulphide, giving rise to the mineral chromite or daubreelite and leaving no Cr for the nickel-iron).

Although these experiments only make it possible to form an approximate estimate of the amount of chromium present in these aerolites it would seem to lie between o'6 per cent and o'i per cent.

In the previous experiments the proportion of nickel which was kept the same in all mixtures was evidently in considerable excess of that contained in any of the aerolites; the experiments were therefore continued, blocks made in the same way as in the experiments with chromium were used as electrodes for the arc. The proportion of nickel was from 2 per cent down to o'04 per cent-photographs of the spectrum were made under the usual working conditions. The portion of the spectrum taken was that containing the chromium group, A 3578-840,

system.

From the results of my unfinished notes on the spectrum analyses of meteoric irons, to which I have already referred, it would appear that either the siderites are of a different origin, or that they have constituted the solid nucleus or core, from which by some process at present unknown the chromium and other elements had been separated, leaving the magnetic elements iron and nickel as the familiar ferro-nickel meteorites.

IS THE ELECTRICAL CONDUCTIVITY OF THE ELEMENTS CONDITIONED BY THE PRESENCE OF ISOTOPES?

A SUPPLEMENTARY NOTE.*

By F. H. LORING.

If the percentages of isotopes, which were given in my previous paper, be plotted additively with the resistivities, also given, a straight-line curve is obtained, showing a relation which seems to imply that the theory of whole. number isotopes as applied to the ordinary elements is not without some foundation of fact. The accompanying diagram shows the relation.

in not fitting in with the percentage rule suggested, but as Commenting on the diagram, cadmium is an exception there is a peculiarity in Northrup's temperature-resistance

To be read in conjunction with my paper in the CHEMICAL NEWS, July 11, 191, cxix., 14.

curves for zinc and cadmium, and the curve of the former is not confirmed by Tsutsumi, the value for cadmium may be queried. Should, however, the abnormal characteristic of cadmium eventually be established, then a closer study of the exception might prove of interest. Gallium contracts on melting, and the resistance of this element in the state of maximum density close to the melting-point is 27.2 X 10-6 (A. Guntz and W. Broniewski, Comptes Kendus, cxlvii., 1474). Plotting 50 per cent-which is the most regular value involving an isotopic proportion of

continuity to the curves Banic. The choice of resistivity is, however, in accord with the principle of nearest state, since there is likely to be nearer comparableness if the values be taken when the elements are in their most dense state at fusion. The example of gallium given above makes this point clear. The plotted values for the resistivities of cadmium, tin, and lead are those of Northrup (loc. cit., previous paper). Tsutsumi's values for tin and lead are respectively 23.8 and 48 1. There is therefore little to choose between the values of these investigators. The

5 to 5 as given in the CHEMICAL NEWS (1914, CX., 25)on the foregoing value gives one that falls exactly on the straight-line curve B. The resistivity of thallium at fusion is obtained from Vincentini and Ómodei's paper (Atti. Accd. Torino, 1889-90, xxiii., 30), but these investigators give no series of values which can be plotted, so that some uncertainty obtains with regard to the use of the single value calculated from the data given.

It will be seen that in those cases in which the -0values are taken (see inset diagram) the percentages for the lower-mass isotopes are selected in order to give

vaiue for arsenic at Q is, perhaps, what one might expect as obtained under suitable conditions necessary to impart to this element the proper state for comparison if this be possible.

The relation plotted can be expressed mathematically thus:

Let x1 = periodic place as shown in the diagram, numbered J, 1, 2, &c., up to 9; for Cu, Ag, Au, Zn, Cd, Hg, Ga, In, Tl, and Ge.

Let x2 =

periodic place, numbered o, 1, 2, &c., starting at tin = 0; for Sn, Pb, As, Sb, Bi, &c.

Let r = the specific resistance or resistivity at the melting-point when the density of the element is the greatest. The 10-6 multiplier may be neglected in these calculations.

Let p the percentage of higher-mass isotopes for the (0) resistivities, or the percentage of lower-mass isotopes for the (--) resistivities (see inset diagram). Then

23'3+9x1 Yi = pitr,

this equation being for the elements from copper to germanium inclusive, as shown in the diagram, and—

3×233+3×9x2 = Y2 = P1+r,

this equation being for the elements from tin to bismuth inclusive, no attempt being made to extrapolate beyond bismuth.

= 10

The original plotting is such that one group-place mm., and the percentage and resistivity values are on the scale I mm. one whole number.

Groups III. and V. are joined by a line (d) to indicate that possibly all the element of these two groups contract more or less on passing from the solid to the liquid state, as is known to be the case with gallium, antimony, and bismuth.

Referring to the CHEMICAL NEWS (1915, cxi., 13), the is topic proportions for gallium, indium, tin, and lead should be taken respectively, 5 and 5, 7 and 6, 7 and 8, 10 and 9, to have percentages in agreement with the rule berein given, and when this is done the isotopic proportions, or "atom-numbers" as originally termed, form a regular numerical set of sequences throughout the section of the periodic table under consideration, but in the case of tin the lower atomic mass percentage (46.6) fits on the straight-line curve when plotted from the resistivity value 23. This may represent a wrong procedure, as it would seem to imply that tin was similar to antimony and bismuth, whereas it resembles lead in its resistivity characteristics. The higher percentage, 53'3, is perhaps the correct one to use, and when a better measurement is

made of tin this point can be reconsidered. The resistivity, to agree with the higher percentage, should be about 17. The lowest experimental value is about 21. It should be noted that the above numbers which appear to require a revision on account of the new relation, were queried in the above communication. All the other isotopic-proportion numbers herein used are the same as originally given. The theory of conduction is of possible interest in connection with the apparent atomic relationships shown, for consider a small-mass nucleus so close to a large-mass nucleus that the electronic orbits combine (or nearly combine) to form a figure eight, the electrons tending to leave the former to pass round the latter owing to the greater attraction of the larger mass. Overloading the circuit electrically at any point might then give rise to a progressive flow of electrons from atom to atom. On cooling the metal, a point might be reached when further cooling (contraction) would not improve the contiguity of the orbits, so that perfect conductivity of electricity without any oscillation or vibration of the atoms (beat or CR loss) might take place at a temperature just above absolute zero.

The strength of the original acid may be a factor in this case. On raising the cover at infrequent intervals during the reaction, a faint odour of nitrogen peroxide was noted. The resulting solid is partly if not wholly aluminium hydrate, as it failed to deflagrate.

So far, it seems that nitric acid does not combine with the metal to form a normal salt, but slowly converts it into a bydrate.

As to double salts, it is to be regretted that references to them are so few, far between, and even meagre (to judge from common text-books); moreover, e.g., in Watts, vol. i., p. 146, col. 2, we get no more than this:-" Very many Al salts also form double salts; the most characteristic of which are the alums," and 22 lines at p. 426, vol. iv. A double chloride of Fe and Al recently rewarded the writer's efforts. It took the form of tabular crystals, about 3 mm. square, of a delicate apple-green and was somewhat deliquescent as damp weather approached.

ADDENDUM. Since the above was written, this salt has proved unstable. With a further slight increase in general humidity the salt has broken down, the solid remaining being mostly ferric oxide.

Obviously the formula of this double salt, its water of crystallisation, and refractive index, &c., bave yet to be determined.

CHEMICAL ACTION PRODUCED BY RADIUM

EMANATION. II.*

THE CHEMICAL EFFECT OF RECOIL ATOMS. By S. C. LIND.

1. Introduction.

velocity of combination of hydrogen and oxygen gases IN Part I., the preceding paper, it was shown that the at ordinary temperature, under the influence of radium by following the reduction in pressure at constant volume. emanation mixed with them, can be conveniently measured An apparatus suitable for this purpose was described, and data were given proving the applicability of a kinetic equation based on the assumption that in a given limited volume the reaction velocity is proportional to the amount of emanation E present at any time and the gas pressure P, both variables, the latter varying as a function of the former.

the volume of the containing vessel as well as on the The change of pressure produced is also dependent on quantity of emanation. In small vessels, say a sphere of 1 cm. diameter, owing to the limited quantity of gas, the pressure falls very rapidly (unless the quantity of emanation be extremely small), so that a condition is soon reached in which the layer of gas traversed by an a-particle the same condition can be attained in larger chambers, becomes very thin, the order of a few mm. Of course, but is not reached, starting from normal pressure, without volume of gases to be acted on before the pressure sinks to much larger quantities of emanation, owing to the greater

low values.

On attempting to apply the same kinetic equation to the velocity observed in a 1 cm. sphere, as had been found

By E. RATTENBURY HODGES.

IN "Watts' Dictionary" (Second Edition, 1890) it is stated at p. 142, col. 2, that "concentrated or dilute nitric acid has no action on Al." This appears to be incorrect. "The time-element" must in this, as in other cases, be

taken into account. After exposing Al foil to the action of the slightly diluted acid for seven or eight weeks I found that nearly all the metal dissolved, to form, not a definite salt, but after slow evaporation, a light grey and somewhat colloidal mass with some free acid in it.

but a value which rose rapidly as the pressure diminished. This puzzling discovery could not be explained by the action of a-rays alone, but an analysis of the results suggested that it could be explained on the assumption that the "recoil atoms" produce chemical action proportional to their ionisation, just as the a-particles do.

It may be profitable to consider briefly something of the When an atom, like Ra A properties of "recoil atoms." or Ra C, emits an a-particle, the residual atom recoils with

* Published with permission of the Director of the U.S. Bureau of Mines. From the Journal of the American Chemical Society, xli., No. 4