THE NATURE OF THE a PARTICLE. By Professor E. RUTHERFORD, F.R.S., and T. ROYDS, M.Sc. THE nature of the a particle from radio-active substances has, for several years, been one of the most important questions in Radio-activity. The evidence as a whole indicates that the a particle is an atom of helium carrying a positive charge. Recent experiments of Rutherford and Geiger (Proc. Roy. Soc., 1908) have substantiated this conclusion. An additional proof of the correctness of this point of view is afforded by the good agreement between the rate of production of helium calculated by Rutherford and Geiger, and the rate of production recently measured by Sir James Dewar (Proc. Roy. Soc., 1908).

This evidence is, however, of too indirect a character to prove decisively that the a particle is an atom of helium. It might be possible, for example, that the expulsion of an a particle led to the liberation of helium from the active matter, but that the a particle itself was not an atom of helium. In order to give a definite proof of the identity of the particle with a helium atom, it is necessary to show that helium can be obtained from accumulated a particles, quite independently of the active matter from which they are expelled. This has been done in the following way :Purified emanation, corresponding to the equilibrium amount from 150 mgrms. of radium, was compressed by raising a column of mercury into a fine glass tube about 15 cm. long. The walls of this glass tube were sufficiently strong to withstand atmospheric pressure but thin enough to allow the greater part of the expelled a particles to be fired through them. After a number of trials, Mr. Baumbach succeeded in blowing a number of such fine tubes for us. The emanation tube was surrounded by a larger cylindrical glass tube about 8 cm. long and 1.5 cm. diameter. This was first exhausted by a pump and the exhaustion completed by means of a charcoal tube immersed in liquid air. By means of another side tube connected with a mercury reservoir, the gases formed within the outside tube could be compressed into a small vacuum tube attached to the top and their spectra examined.

The tube containing emanation was about 1/100 mm. thick. The stopping power of the glass for the a particle corresponded to less than 2 cm. of air, so that the a particles expelled from the emanation itself, radium A and radium C escaped through the emanation tube, and were fired into the walls of the outer glass tube. Twenty-four hours after the introduction of the emanation, no trace of helium was detected on compression of the gases into the vacuum tube; at the end of two days the helium yellow line was seen faintly; after four days, the yellow and green lines came out brightly, and after six days practically the whole helium spectrum was observed.

An experiment was then made to test whether the helium observed could have diffused from the emanation through the thin glass walls. For this purpose, the emanation was replaced by about ten times its volume of helium and a new outer tube and vacuum tube placed in position. No trace of helium was observed in the outer tube over a period of eight days. Emanation was again introduced, and after four days the helium spectrum was again observed.

In these experiments every precaution was taken to prevent possible contamination of the apparatus with helium. Freshly distilled mercury and fresh glass apparatus was used. No trace of helium was observed unless the emanation was introduced into the fine capillary.

TANTALUM AND NIOBIUM IN AUSTRALIA. By EDWARD S. SIMPSON, B.E., F.C.S., of the Geological Survey of Western Australia.

IN the census of minerals of Australia submitted to the Australasian Association for the Advancement of Science in 1890 no mention is made of any mineral containing tantalum and niobium. Since then, however, these rare metals have been recognised in several widely separated districts in the Commonwealth, and, in response to the recent commercial demand for tantalum ores, deposits of great richness and extent have been disclosed in the Pilbara Goldfield of Western Australia. In this paper an account will be given of the discovery of these interesting minerals in Australia, their mode of occurrence, and their chemical and physical characteristics.

General Features of Occurrence.

Before dealing with purely Australian deposits, it will be well to go briefly into the general features of the question.

These two metals are nowhere found in the native state, nor in sulphide or other similar minerals, but exist always in combination with oxygen and one or more other metals, the oxides having an acid character, and giving rise to tantalates and niobates. They invariably occur in conjunction, replacing one another isomorphously to a very variable extent, the niobate of a metal often passing by insensible gradations into the tantalate without change of form or physical characters other than a corresponding gradual rise in specific gravity, tantalum having an atomic weight double that of niobium. In this article, therefore, whenever a mineral is described as a tantalate it must be understood that it contains niobium as well as tantalum, but that the former is present in preponderating amount, and vice versa.

The ores hitherto detected in Australia are:

1. Columbite, niobate of iron and manganese. 2. Tantalite, tantalate of iron and manganese. The subspecies manganotantalite contains more manganese than iron; the normal variety more iron than manganese.

3. Stibiotantalite, tantalate of antimony. 4. Microlite, tantalate of lime.

5. Euxenite, titanoniobate of yttrium, erbium, cerium, &c. Until recently the best-known localities of the mineral tantalates and niobates were Sweden, Norway, Bavaria, Siberia, Greenland, and the United States. Though occasionally recorded as occurring in syenite rocks, the most usual primary occurrence in all these countries is in pegmatite veins in granite, especially in those characterised by the presence of much albite. In these veins they are commonly accompanied by quartz, orthoclase, and mica, as well as albite, whilst garnet, zircon, topaz, monazite, cassiterite, and other uncommon minerals are often present. The only primary deposits described so far in Australia are those of Finniss River, (Northern Territory), Greenbushes (Western Australia), and the Wodgina District (Western Australia), all areas of granitic rocks.

Most native tantalates and niobates offer considerable resistance to chemical change, and, being in the main both hard and tough, are of frequent occurrence in detrital deposits, though usually overlooked unless the latter happen to be worked for gold or tin. Still, there are numerous records of their detection in stream deposits in

CHEMICAL NEWS,}

Jan. 29, 1909

In a parcel of stream tin ore in the museum of the Geological Survey of Western Australia is a single fragment of a mineral forming a quadrant of a sphere I in. in diameter, with radiated crystalline structure. This mineral is of an intense black colour, with a metallic lustre, and specific gravity 7.3. It is identical in appearance with some of the ore from Wodgina, and is without doubt manganotantalite. It is an aggregate of a number of wedge-shaped crystals, the mass parting readily along radial planes on being struck. Closely attached to its outer surface are numerous small fragments of quartz and several fragments of much altered albite. These indicate the original source of the mineral to have been those quartz-albite pegmatite veins which form the matrix of the cassiterite.

Another similar, but smaller, fragment occurs in a second sample of stream tin ore, and others still smaller may easily have been overlooked.

Cooglegong. This tinfield occurs thirty miles to the southwest of Marble Bar. According to the researches of Mr. | A. Gibb Maitland, it is situated in the midst of a large area of granite, which, in places, is gneissic. "The granite is intersected in certain localities by veins of pegmatite, which have doubtless been the original source from which the stream and residual tin have been derived."

Gadolinite has been found both in the stream deposits and, associated with cassiterite and monazite, in a pegmatite vein.

In a paper on this occurrence of gadolinite, read before the Royal Society of New South Wales, in October, 1902, Mr. B. F. Davis says:-"Amongst the minerals I brought from the north-west I have two varieties of a mineral allied to 'euxenite' in physical characteristics, as described by Dana. One differs from the other in having more manganese in the place of uranium. They are essentially niobates and titanates (with tantalum) of uranium iron and yttrium earths, with cerium earths and thorium. They occur with cassiterite and monazite in the wash-dirt. I have only a few small pieces, but one mineral at least was not uncommon. I saw it in all the tin ore bagged from different parts of the country,"

Some of the mineral from this same locality, collected from samples of tin concentrates by Dr. McKenzie, of the Tin Smelting Works, Sydney, has been examined by Mr. D. Mawson, and found to be strongly radio-active.

It is not, however, at all clear from Mr. Davis's paper whether this mineral was really obtained at Cooglegong or not. It may possibly have come from Moolyella.

I have recently come across some specimens in the West Australian Museum, the locality of which is given as the Shaw River, so that they come either from Cooglegong or from the Old Shaw Tinfield a few miles out of Cooglegong. These specimens consist of a number of angular detrital fragments of typical euxenite, varying in size from 10 to 40 mm. in length, and coated externally with a brown clay. On a fresh fracture the mineral is brown in colour, and possesses a brilliant resinous lustre. It has a specific gravity of 5.3.

Thelemann's Find.—Sixteen miles north-west of Lalla Rookh tantalum ore was obtained in 1906 by Mr. F. Thelemann. It is detrital ore, and is said to occur only in limited quantities. It is of little commercial value, being a low-grade iron columbite, assaying from 3 per cent to 5 per cent of tantalic oxide. One sample, consisting of more or less worn fragments from a quarter to 1 inch in diameter, contained 4'92 per cent of tantalic oxide, 70'34 | per cent of niobic oxide, and no tin. The specific gravity of the constituent fragments was very uniform, averaging 5.5. The ore from this locality is frequently well crystallised. One good crystal measuring 7 × 23 x 30 mm., and having a specific gravity of 5'53, shows the following faces :a, 100; b, 010; c, 001; #, 133; e, 021; m, 110; g, 130; The lower half of this crystal has not developed, having apparently formed against an already crystallised mass of albite. Several other crystals, with fewer faces, have been collected from this locality. Many are not of

y, 210.

51

the tabular habit of the crystal described. All are, how. ever, of low specific gravity, indicating a low tantalum content. One fragment has the radiated spherical structure previously mentioned in connection with Moolyella. The only associated minerals observed were quartz, tourmaline, and albite. Granite is the prevailing rock in the locality. Green's Well.-The main workings in this district are situated at a locality variously known as Green's Well, Mount York, and Chingamong. They were first developed in 1905, and are situated in the same belt of granite as extends from Thelemann's Find through Wodgina to Mount Francisco.

The original mine in this locality has been described officially in the following terms :-"On M.L. 100 (O. T. Bell and party) a rubbly felspar formation has been exposed for a few feet. This carries tantalite, but sufficient work has not been done to allow of an opinion as to the richness of the lode. On McBeth's alluvial reward claim tantalite can be easily seen in the gully that traverses the claim.”

A sample of dressed ore from Green's Well, brought to Perth by Mr. A. Gibb Maitland, apparently consists of both stream and lode ore in angular fragments from I up to 20 mm. in diameter. A great portion of it is more or less well crystallised, a few excellent crystals being observed in it, of which the following are details:

The sample, as a whole, assayed-tantalic oxide, 42'39 per cent; niobic oxide, 21-09 per cent; metallic tin, 15.62 per cent. The mineral itself varies from a columbite, with specific gravity 5'35, to a tantalite, with specific gravity 6.84. For the most part it has a dull rusty-black surface, but occasional crystals exhibit brilliant black metallic faces, especially a. This face and b is often striated vertically. The only associated mineral observed in any abundance is cassiterite. The primary deposit from which the ore is derived appears from the above description to be a typical quartz-albite pegmatite.

The ore from Green's Well is characterised by the very variable extent to which tantalum and niobium replace one another. In another sample from here, individual crystals varied in specific gravity from 6.4 up to 7:7, indicating an approximate percentage of tantalic oxide varying from 46 to 81.

Wodgina. By far the most important tantalum deposits in Australia are those of Wodgina, situated in the Pilbara Goldfield, in lat. 21° 15′ S., long. 118° 40′ E., 90 tons of dressed ore having already been shipped from this locality.

In a recent article in the Mining Journal, Messrs. F. H. and W. A. Mitchell (the latter assayer at the Mons Cupri Copper Mine, 80 miles from Wodgina) make the following statement with regard to the first discovery of tantalum ore at Wodgina :-"This mineral was first observed by us in North-West Australia early in 1901, when a crystal was submitted to the British Museum authorities for confirmation; but it was not until about four years later that we introduced this mineral into Europe for commercial purposes."

In May, 1904, a black mineral from this locality was forwarded for identification to the Acting Mineralogist and Assayer, Mr. C. G. Gibson, and proved to be manganotantalite, a preliminary analysis showing the presence of 80 per cent of tantalic and niobic oxides and 16 per cent of manganese oxide. At that time there was no market for the mineral except for museum and other educational purposes, for which purpose the demand was limited to a few pounds per annum. Towards the end of the year, however, the demand which arose in connection with the

The locality has recently been geologically examined and mapped by Mr. Maitland, and from his report the following resumé of the structural features of the rock masses and ore bodies has been culled.

The tantalum ores occur in stream deposits, in shallow surface detritus in the immediate vicinity of the outcrops of pegmatite dykes, and in these dykes themselves. They occur in a mass of hornblende-schist, and are apparently offshoots of a mass of granite lying at a short distance to the north, east, and south-east. Between the hornblende

rock and the granite on the south-east are a series of schists of indeterminate origin, mostly very siliceous and carrying either mica or hæmatite. Their origin is still a matter of some speculation. Within the area of these schists the pegmatite veins are tin-bearing, and are being worked for that metal.

The most important tantalum vein in Wodgina proper is that which passes through mining leases 86 and 87 in a north and south direction. It is from 30 ft. to 40 ft. wide, and consists of variable proportions of quartz, felspar (mainly albite), mica (muscovite and lepidolite), and tantalite; the last-named in crystalline masses from the size of shot up to 5 cwt. in weight. A little west of this main vein is a second smaller one of similar nature. From the outcrops of these veins a larger amount of ore has been shed, and the greater part of the ore hitherto exported has been obtained by "specking" and dryblowing the shallow detritus on the surface. About 71 tons is said to have been obtained in this way.

The main vein appears to continue for about a mile north, where it is 20 ft. wide, and has there also been worked for tantalum.

Since Mr. Maitland reported on this field other tantalumbearing dykes have been opened up in the vicinity, and ore is still being obtained from shallow surface soils, as

well as from true alluvial deposits in the many small

valleys.

(To be continued).

THE OSMOTIC PRESSURE OF CONCENTRATED SOLUTIONS, AND THE LAWS OF THE PERFECT SOLUTION.* By GILBERT NEWTON LEWIS. (Continued from p. 42).

The Law of Ideal Solutions.

WHAT We shall call a perfect or ideal solution is somewhat a matter of choice. We might define as an ideal solution one which obeys the law of van't Hoff, or the modified form of this law proposed by Morse and Frazer, or the law of Raoult, or the law of Henry. These laws are essentially identical for the infinitely dilute solution, but for a solution of finite concentration we are at liberty to choose one but not all of these laws to define the ideal solution. No one of them is true for every solution at every concentration, and we must therefore choose that one which holds most nearly for the greatest number of substances over the widest limits of concentration.

I shall attempt to show that the most fundamental law of solutions and the one by which the perfect solution is best defined is the following modification of the law of Raoult. At constant pressure and temperature the activity of the solvent in a perfect solution is proportional to its mol. fraction. (For a definition of the term activity see Lewis, "Outlines of a New System of Thermodynamic

From the Journal of the American Chemical Society, xxx., No. 5.

=

4;

where is the activity of the solvent in the solution, to the activity of the pure solvent, and N, the mol. fraction, is the number of mols. of solvent in one mol. altogether of solvent and solute. Since, however, the conception of activity is new, and since if the vapour of the solvent obeys the gas law the activity is proportional to the vapour pressure, we may with sufficient exactness for our present purposes, substitute the vapour pressure of the solvent for its activity and writep = poN

5;

that is, in a perfect solution the vapour pressure of the solvent is proportional to its mol. fraction. (The point of view here adopted is practically identical with that which for several years has been advocated by J. J. van Laar in numerous publications). Thus in a solution containing o'i mol. solute to og mol. solvent, N = 0.9 and the vapour pressure of the solvent should be nine-tenths of its vapour pressure in the pure state, or if the solution contains o 25 mol. solute to o 75 mol. solvent, should be o 75 po. This is simply a statement of Raoult's law in its simplest form.

immediately to a simple equation for the activity or the (NOTE. It is important to note that Equation 4 leads us In the paper previously vapour pressure of the solute. referred to I have proved the following exact equation for the change in the activity of each component of a binary mixture with change of composition, namely

where K is a constant. We see, therefore, that in a perfect solution it is also true that the activity of the solute is proportional to its mol. fraction. If we substitute pi the vapour pressure of the solute, for §1, p1 = KN1, which is, in a slightly modified form, the law of Henry. In other words, if both vapours obey the gas law, the law of Henry may be derived thermodynamically from the law of Raoult and must hold if that law does).

There are no cases in which the law of van 't Hoff or the modified form of this law proposed by Morse and Frazer have been shown to hold at concentrations higher than normal. (In a normal solution in water the mol. fraction of the solute is about 0.02).

Indeed, at very high concentrations van 't Hoff's law cannot hold, for the osmotic pressure of a solution approaches infinity as the percentage of solvent approaches zero, while the osmotic pressure calculated from the van 't Hoff equation never exceeds a few hundred atmospheres even when we approach the condition of pure solute. On the other hand, it will be shown presently that the law proposed by Morse and Frazer ordinarily gives, at higher concentrations, osmotic pressures far higher than those which actually exist. But often the law of Raoult (and the modified law of Henry) has been shown to hold at all concentrations from o per cent to 100 per cent of solute, and while in many other cases this law does not hold, the greatest deviations are always found in those cases in which we have reason to believe that the solvent and the solute form complex compounds either with themselves or with each other.

Many illustrations might be given to show the remark

able scope of Raoult's law. I will choose a binary mixture which has been studied more carefully over a wide range of concentration than any other, namely, benzene and ethylene chloride. The vapour pressures are taken from the excellent paper of Zawidski (Zeit. Phys. Chem., 1900, xxxv., 129). We will call benzene the solvent and ethylene chloride the solute. In Table III., in which the data marked by Zawieski as questionable are omitted, the first column gives the number of grms. of solute to I grm. of solvent, the second gives the partial vapour pressure of the solvent at 50°, and the third gives the molecular weight of ethylene chloride calculated from the vapour pressures by Raoult's law. The calculated molecular weights are constant, even up to the highest concentration, where the solute constitutes over 90 per cent of the solution. The average of these calculated molecular weights is 99.1, while the actual molecular weight of ethylene chloride is 990. (We have therefore every ground for believing that also in the pure state ethylene chloride exists in the form of simple molecules).

Grms. C2H4Cl2 to i grm. C6H6.

TABLE III.

H

G

53

If then we define a per ect solution as one which obeys Raoult's law, it is interesting to find what the law is connecting osmotic pressure and concentration in a perfect solution. This law, which is less simple than either the law of van 't Hoff or that of Morse and Frazer, may be derived directly from Equations 3 and 5, and is—

7,

2

Vo

The Technical College, Derby.

where Vo is the molecular volume and a the compressibility of the solvent.

(To be continued).

AN APPARATUS FOR SIMULTANEOUSLY EXTRACTING A SOLID AND FILTERING THE SOLUTION SO OBTAINED.

By FREDERICK RECORD, B.Sc.

IN the CHEMICAL NEWS of June 12, 1908 (vol. xcvii., p. 280) there appeared a drawing and description of a form of apparatus for the above purpose, which consisted wholly of glass, and which had the disadvantage of requiring considerable skill in its construction. The accompanying section shows a modification of the apparatus which can be made much more readily. The inner tube, A, is contracted at its lower extremity, and has a pair of diametrically opposite holes, c, in its walls; it is held in position inside the outer tube, в, by means of a cork, H; E is a filter disc which is covered with a layer of filter-paper and * Strictly speaking, we define a perfect solution as one which obeys Equation 4 rather than Equation 5, but the more precise method which employs the activity instead of the vapour pressure leads to exactly the same equation for the osmostic pressure as we shall derive here.

THE PRESENCE OF A CHOLESTEROL SUBSTANCE IN SOILS: AGROSTEROL.*

By OSWALD SCHREINER and EDMUND C. SHOREY.

IN the attempts which have been made to isolate definite organic compounds from soils it has been found that in most cases treatment of the soil with alcohol even at boiling temperature does not give a solution of soil organic matter from which definite results could be obtained.

However, with some soils, characterised usually by a high content of organic matter, this treatment has led to the isolation and identification of definite organic compounds. The details of the method and the properties of one of the compounds obtained are the subject of this paper.

The soll from which this compound was obtained was the Marshall clay from North Dakota, a black soil containing 10.6 per cent organic matter and 0.51 per cent nitrogen.

When this soil was treated with boiling 95 per cent alcohol there was obtained a greenish brown coloured extract, from which, on cooling, a yellowish microcrystalline precipitate separated. On treating the soil with successive portions of boiling alcohol, the extracts, combined and

* Presented at the New Haven Meeting, June, 1908, of the American Chemical Society, by permission of the Secretary of Agriculture. From the Journal of the American Chemical Society, xxxi., No. 1.