If chloroform is used as the solvent, decomposition is more rapid, but it must be noted that chloroform is itself decomposed in the presence of light, while carbon tetrachloride is not affected.

NOTES FROM FOREIGN SOURCES.

RECENT ATTEMPTS TO SEPARATE

ISOTOPES.*

BY A. PINKUS.

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Ever since the first researches in radio chemistry were performed, and long before K. Fajans and F. Soddy had clearly stated the problem of isotopy, this disconcerting characteristic of certain radioactive elements had revealed itself—the absolute identity of the most diverse chemical and physical properties in spite of different atomic weights and a definite power of disintegration. The phenomenon was at first regarded as exceptional and limited to the radioactive elements, but was perceived to have a much more extended significance. Thus, in 1913, J. J. Thomson's researches on the spectrum of neon and the discovery in the following year of the varieties of lead of different combining weights proved the complex nature of these two inactive elements. Thomson's method of analysis, perfected in 1919 by F. W. Aston, so as to give the masses of the carriers of charges correct to onethousandth, has enabled this result to be confirmed as regards neon and to be tended to nine other ordinary elements--chlorine, argon, mercury, krypton, xenon, boron, silicon, bromine and nickel. Thus isotopism appears to be a normal phenomenon, exhibited by many ordinary chemical elements. This result acquires a special importance in view of the fact that all the mass spectra, with the exception of that cf hydrogen, give whole number atomic weights both for the simple elements and for the constituents of elements recognised as complex. The following table gives Aston's latest results for complex ele

ments:

ex

*Abridged from the Journal de Chimie Physique, XIX., 4, 336.

(The numbers in brackets are not regarded by Aston as definitely established).

As the domain of isotopism enlarges, the question of the separation the separation of isotopes acquires increasing importance, especially for inactive elements such as chlorine and mercury for example, the complex character of which has been revealed only by the positive ray method, and which seem to exist in nature only in mixtures which are always identical. The electromagnetic method, moreover, only leads to indeterminable quantities of simple separated atoms, and hence cannot be used in the comparative study of their properties. It does not appear to be of very general application and is very unreliable, at any rate as employed at present, in the case of the many elements which have a low vapour tension and which do not yield stable volatile compounds. In the case of these elements, attempts at direct fractionation remain the only means at present of investigating isotopism.

Any method of fractionating mixed elements must evidently be based upon the sufficiently accentuated non-identity of a given property of the isotopes. The first to be studied were naturally the chemical and electrochemical properties which, according to the older views, could not be the same for two elements of different atornic weights. All attempts hitherto made in this direction have always been a complete failure, and it is just this failure which has largely contributed to the development of the theory of isotopism. The failure led to the conclusion that only methods depend

ing upon the atomic mass could lead to positive results. But in the light of certain modern theories this conclusion has largely lost its restrictive value. Actually in Rutherford and Bohr's model of the atom the mass of the nucleus would certainly have some influence, however slight, upon the configuration and frequencies of the outer electrons, so that even the properties, the origin of which is in the superficial layer of the atom, would show certain differences in two isotopic elements. At the present moment, our knowledge is not sufficient to enable us to foretell with certainty the magnitude of these differences. Hence a method of separation which is applicable to ordinary elements cannot a priori be regarded as absolutely useless in the case of isotopic elements. Experience has to decide in each special case.

Experience has already decided in the negative in the case of fractionation, based upon a difference of chemical affinity, electrochemical properties, solubility,

vapour tension in the solid or liquid state. All these methods appear to be definitely abandoned to-day. On the other hand, special methods have been tried or suggested, and some of them have finally given, especially during the last two years, positive results which seem to be definitely established.

The attempts to separate isotopes, the results of which have been published in 1920 and 1921, have depended upon the three following methods:

I. Action of Centrifugal Force.

II. Diffusion in the Gaseous State.

III. Evaporation under reduced pressure followed by an immediate condensation of the vapourised molecules.

The first of these methods is based upon the proportionality between the densities and the atomic weights of the isotopes. The efficiency of the method was discussed in 1919 by F. A. Lindemann and F. W. Aston, according to whom centrifugation of liquefied neon (regarded as a mixture of two isotopes of atomic weight 20 and 22), or of fused lead (regarded as a mixture of Pb U and Pb Th of atomic weight 206 and 208), performed in suitable conditions and

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with a peripheric velocity of 10 cm. second would lead to differences of the order of 0.5 per cent. between the densities of the portion nearest to and that furthest from the centre of rotation. The method was applied in 1920 by J. Joly and J. H. J. Poole to the separation of Pb Th and Pb U, the atomic weights and densities of which show a difference of about 1 per cent. The experiment was carried out with ordinary fused lead contained in steel tubes heated electrically placed upon a centrifuge turning 150 times per second. The tubes were 6 cm. long, the distance between the centre of rotation and the nearest extremity of the tube was 4 cm., which corresponds to a peripheric velocity of about 9.4 x 10 cm. per second. After an hour's centrifugation, the metal was rolled into spheres, as homogeneous in structure as possible, and the densities of the speci

thus obtained were compared by successive weighings in air and methyl iodide. The determinations of the density were made to 0.003 per cent. about. The results of five experiments showed that the sphere coming from the lower end of the tube was in three cases denser than that coming from the upper end (differences 0.05, 0.006, 0.01 per cent.), in one case it was less dense (difference 0.003 per cent.), and in one case the density was the same. These results indicate that no separation has been proved. The calculations of Lindemann and Aston referred to these experimental conditions would only foretell a difference of 0.005 per cent. between the two spheres. In spite of these negative results it is probable that the centrifugation method will not be abandoned. According to J. H. J. Poole, it will only be necessary to increase the velocity of rotation about seven times with the same experimental arrangement in order to obtain clearly detectable separations. In the case of mercury, for example, considered as a mixture of isotopes of atomic weight 200 and 204, in these conditions the differences of density obtained would be 0.15 per cent., and the calculated results are even more favourable in the case of neon. (To be Continued.)

PHOSPHORUS IN CALIFORNIAN PETROLEUM.

CHASE PALMER.

Operators in oil fields already realise the importance of knowing something of the

composition of underground waters, but the general impression seems to be that nothing more is needed than a statement of the items employed to determine the fitness of a water for use in a steam boiler. Consideration of the composition of oil field waters is confined almost wholly to the major constituents of such soluble minerals as common salt, glauber's salt, gypsum and soda. Little evidence concerning the minor constituents of oil field solutions has been sought, and it is not surprising, therefore, that in the waters of the oil measures of California phosphates have escaped observation. If the prevailing opinion is correct, namely, that phosphates in all waters are derived only from the mineral, calcium phosphate, dissolved with difficulty out of the adjacent rocks. and sands, then, of course, the minute quantity of phosphate possible in an oil field solution can have little significance and may well be disregarded. If, on the other hand, phosphorus can be found in the oil with which these subterranean solutions have been in contact, then the importance of knowing the phosphate content of an oil field water is apparent.

On a single section of the Sunset district, California, five well waters presumably from the same oil sands were found to contain phosphates in quantities ranging from 0.4 to 2.6 parts of phosphates (PO) in one million parts of solution. Although all of these solutions are primarily brines, some of them are modified chiefly by interaction with oil while others are mixtures containing also waters intruding from outside the oil measures. The persistence of phosphate in these waters suggested the possibility that phosphorus might also be present in the oil of that locality. Consequently a heavp oil from the same section that produces the phosphate solutions was closely examined and found to contain phosphorus to the amount of one hundredth of one per cent. of its weight. Another heavy oil drawn from a shallow well in the Kern River oil field also showed a phosphorus content of one one-hundredth of one per cent. This well has been producing oil for several years.

one

NITROGEN COMPOUNDS IN CALIFORNIAN PETROLEUM.

Phosphorus and nitrogen in the properties of their compounds resemble each other closely, and since nitrogen com

pounds constitute a large part of a Californian crude oil, consideration of the chemical nature of these nitrogen pounds may throw light on the source of phosphates in oil field solutions.

com

Californian petroleums consist essentially of three very different classes of organic compounds, namely, hydrocarbons, hydrocarbons with sulphur, and hydrocarbons with nitrogen. The nitrogenous hydrocarbons are usually called organic nitrogen bases. Members of all of these classes are oxidizable, but their oily nature shields them from direct attack of inorganic oxidants mobile in the waters or fixed in the rocks. The organic nitrogen bases, however, form soluble salts with strong acids so that considerable quantities of these nitrogen bases are undoubtedly dissolved by the corrosive waters of the oil measures and the resulting solutions of organic nitrogen salts, necessarily in a state of high dilution, can offer little resistance to the attacks of oxidants. In 1899 Mabery1 prepared a long series of organic nitrogen bases by digesting an oil from Santa Paula, California. More recently Mabery and Wesson have shown that under certain conditions an inorganic oxidant, like potassium permanganate, oxidizes these organic nitrogen bases to organic nitrogen acids. while under other conditions ammonia is formed. Appreciable amounts of ammoniacal compounds and of organic nitrogen acids are therefore to be expected in a water closely associated with a Californian oil. The organic acids obtained by Mabery are derivatives of pyridine, an important constituent of bone oil produced by distilling the bones of vertebrates.

2

UNDERGROUND OXIDATION.

When nitrogenous organic matter decays under atmospheric conditions nitrites and nitrates are among the final oxidation products and surface waters polluted by decomposing organic matter often contain nitrogen in all the four forms that have been mentioned. It is a striking fact that these aqueous solutions brought up by the wells, solutions which have reacted with the oils underground and are charged with ammoniacal salts and organic nitrogen acids, have failed to show the presence of nitrates and nitrites. The organic nitrogen bases of the petroleum, therefore, normally suffer only partial oxidation underground, the limit of oxidation coinciding with the limit which Mabery and Wesson reached by oxidizing the organic nitrogen bases of Santa Paula oil with potassium permanganate.

Manganese dioxide and other oxides of manganese are freely distributed in the oil regions of California. With corrosive brines they would form soluble manganous chloride and halogen which by a cycle of wellknown reactions easily produces active oxygen from the solution. Oil field solutions usually contain manganous chloride formed probably by the reduction of a manganic

NOTICES OF BOOKS.

(1) Roger Bacon, the Father of Experimental Science, by H. STANLEY REDGROVE, B.SC., F.C.S. Pp. 63 + 1 plate. Price 1s. 6d.

(2) Joseph Glanvill and Physical Research in the Seventeenth Century, by H. S. REDGROVE, B.Sc., F.C.S., and I. M. L. REDgrove. Pp. 941 plate. Price 2s.

London:

Wm. Rider & Son, Ltd., 8-11, Paternoster Row, E.C.

(1) It was pointed out in the review of Mr. Redgrove's Alchemy: Ancient and Modern, which recently appeared in The Chemical News, that the lives of many of the alchemists were very interesting, and therefore this life of Roger Bacon by an author so admirably equipped to deal therewith is very welcome.

Roger Bacon was an original thinker, and in his ingenious speculations anticipated many modern discoveries, such as the telescope, microscope, etc. As a result, he has been erroneously credited with some of these discoveries, and a recently discovered MS. in cypher would appear to support the attribution. The authenticity of this MS. is very questionable, and Mr. Redgrove has done well in ignoring it and basing his estimate of Roger Bacon upon his undoubtedly authentic works. did make one discovery in experimental science, namely, that of gunpowder, but his claim to greatness does not rest on this, or on his ingenious speculations, but upon his remarkable grasp of the true nature of the method of science as a combination of experiment and mathematics.

Bacon

The life of Roger Bacon, too, is interesting as an example of the contest between the spirit of science and that of tradition and authority. Mr. Redgrove has chosen an admirable theme, and has dealt with it in a masterly and most interesting manner.

(2) The work on Glanvill may not, perhaps, make so strong an appeal to chemists as that on Bacon, but it deals with the same theme of the conflict of science with the powers arrayed against it in times gone by. Joseph Glanvill was one of the earliest Fellows of the Royal Society. In those days the Society was looked upon with disfavour by those who were pledged to traditional beliefs. Glanvill rendered the Society and the cause of Science great service by his books and writings in defence of the new experimental philosophy.