quantities. Such goods are gradually liquidated, and in many instances the duty paid at the time of importation may not be recovered in full for twelve months, or even longer. For instance, the importer of dutiable goods to the value of £3,000 has to pay £1,000 as duty at the time of importation, and it is not exceptional for the period mentioned to elapse before the whole of the importation is sold and the duty thus recovered. In this way considerable amounts of capital are locked up, to the detriment of the merchant and trade in general. It is submitted that, in the case of reexports, if merchants were given the opportunity of putting goods liable to Key Industry duty into bonded warehouses at the time of importation and thus be relieved of the immediate payment of duty and the uncertainty of obtaining drawbacks, the trade. of this country in re-exports of chemicals would be materially facilitated, and would undoubtedly increase in volume. In the case of sales to buyers in this country, duty would only be paid at the time they were taken out of bond for actual delivery. Under this arrangement comparatively large amounts of capital would be at the importers' disposal, instead of being locked up, as is the case under the present conditions. Consideration has been given, and enquiry made, as to whether there would be objection on the part of warehouse interests to accepting goods scheduled under Part I. of the Safeguarding of Industries Act, on account of their dangerous character in themselves or when stored with other goods. It appears that as these materials are packed in such a manner as to satisfy shipping lines, who accept them at ordinary rates, and, for the same reason, insurance of such goods is effected at low rates, it is believed that warehouse interests would approve of the suggested system of bonding. It is therefore suggested that, as the present system of collection of duties under the Safeguarding of Industries Act, 1921, Part I., is doing great harm to the commerce of this country, especially in the matter of re-exports, the Order made by H.M. Treasury at present in force should be suitably amended so as to allow dutiable goods to be put into bond. Forwarded to H.M. Treasury, and copy to H.M. Customs. B. C. and D. T. A., London, 4th August, 1923. Cast Iron to Resist Sea Water.-A Joint Research with the Electrical Research Association is being arranged to carry out this It is estimated that the important work. experimental work will occupy about two years, and will be carried out at the coast and in tidal rivers. The results of such work will be very beneficial to the electrical industry and our own members. Internal Combustion Engine Castings.This research, carried out jointly by this Association, the Motor Research Association, and the Motor Cylinder Research Association, is reaching a stage when some beneficial results should accrue. cylinders made in this country and abroad have been examined and reported upon. Test castings to variable specifications have been made, and are now being subjected to test. Engine Cast Iron Moulds for Bottle Making.-This joint research with the Glass Research Association is progressing, and test moulds are now being experimented upon and tried in special bottle making machines. Malleable Cast Iron Research.-It should not be necessary to report every month that the progress of this very important work is hampered by the lack of support given by the malleable industry. Malleable iron founders should call a conference and discuss the position of their industry. The Bureau Bulletin gives a complete bibliography of the literature upon malleable iron as published since 1722, which is very uteresting reading. Standard Specification for Grey Iron Castings. The Association considers that the time has arrived when a standard specification for grey iron castings should be drawn up, and steps have been taken to have this carried out in conjunction with the B.E.S.A. PROBLEMS SENT IN BY MEMBERS. Members, during the past month, have sent in problems for the Director's advice upon the following: Porosity in cylinder castings; defects in pump castings; defective pig iron; annealing malleable iron; liners for semi-Diesel engines; C.I. bevel wheels; Cupola design; pumps for sea water; pin-holes in malleable C.I.; shrinkage in castings; malleable annealing ovens; C.I. valve guards; glass bottle moulds; defects in heavy castings; stripping plate patterns; porosity in malleable castings. Take, for instance, Cupola practice: the Association has assisted a large number of members in their Cupola melting methods, yet it is very remarkable to find the very variable conditions under which this is carried out; there is no standardised practice. Here is a wide field for work by the Association and of vital interest to every grey iron founder in the country, and yet, due either to apathy or to the peculiar foundry conservation, he holds out in joining the Association and obtaining its advice. INTERNAL COMBUSTION ENGINE CYLINDER RESEARCH. "The continued examples of failure of metal, not necessarily confined to the marine Diesel engine industry, seem to indicate that metallurgical science either has not reached the high standard which we have lately been accustomed to believe, or the results of investigation in working practice and in experimental research are not communicated in a sufficiently extensive manner to those concerns immediately or indirectly interested. In the case of Diesel engine construction it appears particularly advisable that no efforts should be spared in the direction of further research, and, what is of vital importance, the publications of specifications of alloys, records of experiments with relation to the behaviour of metals in high temperatures, and data referring to wear of parts. "We believe that much time and labour could be saved if there were more co-operation between marine Diesel engine builders, particularly with regard to their experimental sections. Undoubtedly, with such involved subjects demanding investigation, collaboration would benefit the largest concerns equally with the smallest. Definite standards could be set up, guess-work and rule of thumb practices abolished, and data. of exceptional value afforded. With reference to specifications of metal, doubt as to the capabilities of certain types of cast-iron has led to a plethora of costly expedients, by which the designer, bringing to his aid constructional complications, aims at a result which should be attained by more direct and simple means. The present work of the British Cast Iron Research Association should be valuable in this direction." (Motor Ship, June, 1923.) Central House, New St., Birmingham. ROYAL INSTITUTION OF GREAT BRITAIN. WEEKLY EVENING MEETING, FRIDAY, MAY 4, 1923. SIR JAMES CRICHTON-BROWNE, M.D., LL.D., F.R.S., TREASURER AND VICE-PRESIDENT, IN THE CHAIR. THE ORIGINS OF THE CONCEPTION OF ISOTOPES. A Lecture delivered by Frederick Soddy M.A., F.R.S. One of the most important consequences of the study of the chemistry of the products of radioactive change has been the discovery of isotopes and the interpretation in consequence of the Periodic Law in terms of modern views of atomic structure. It is one of the few fields in the vast borderland between physics and chemistry, overrun of recent years by an advancing swarm of mathematicians and physicists, armed with all sorts of new-fangled weapons, in which the invaders have found the chemist already in possession. The broad highways they have hewn thereto are already dusty with the tread of pilgrims, and are being watered by the tears of candidates for "Honours." But the somewhat intricate bye-ways through which the chemist first found his way into this virgin territory, and the views on the road before it was in sight, may stili preserve something of their pristine interest. The word isotope signifies "the same place," In allusion to isotopes occupying the same place in the Periodic Table. Before this word of theoretical meaning was coined, isotopes were experimentally well known as elements non-separable by chemical methods and completely identical in their whole chemical character. The ana lysis of the constituents of matter, to which we were born and brought up to regard as the most searching and fundamental, is an analysis by means of its chemical properties. Although, later, a new and even more powerful method, spectroscopic analysis, was developed, it merely dotted the i's and crossed the t's of chemical analysis, filled in a few vacant places in the Periodic Law, and handed over the newcomers to the chemist to classify along with the rest of the eighty or so "foundation stones" of which he supposed the material universe to be built up. Then, with the close of last century, another new method, radioactive analysis, was developed, which is applicable of course only to the radio-elements-that is, to the elements uranium and thorium and the thirty-four, as we now know, successive unstable products of their spontaneous disintegration. Each of these possesses a definite radioactive character; it is produced from one and changes into another element, and, in both changes, rays characteristic of the two substances are expelled, which are as fine a hall-mark of their identity as any of the "tests" of chemical analysis. But radioactive character, unlike spectroscopic character, is completely independent of chemical character. The latter might be called "existence properties," whereas the radioactive character is that attending the explosion of the atom which terminates the existence of the element as such. It provided the necessary independent method of analysis capable for the first time of distinguishing between elements identical chemically and occupying the same place in the Periodic Table-i.e., between isotopes. THE EARLIER CHAPTER OF RADIO-CHEMISTRY. Not a hint of this, however, was afforded by the earlier chapter of radio-chemistry. On the contrary, no development could appear more normal. Just as rubidium, thallium, etc., were detected by the spectroscope before anything of their chemistry was known, so radium was detected in pitchblende by its radioactivity in concentration thousands of times less than is necessary to show a single line of its spectrum. But with more concentrated preparations a new spectrum was discovered, and then a new element, which was found to possess a chemical character entirely new and sufficing for its separation in the pure state from all other elements. As in the case of the elements discovered by the spectroscope, radium was found to occupy a place, hitherto vacant, in the Periodie Table. But as it happened radium is exceptional in this. Its chemical character was quite normal, and indeed could have been largely predicted beforehand for the missing element occupying this place. The development of the subject showed it to be but one of some thirty-four radio-elements formed from uranium and thorium. But there are not thirty-four vacant places in the Periodic Table to accommodate them. META-ELEMENTS. So far as I am aware, there is no anticipation, prior to the systematic study of the chemistry of the radio-elements, of the idea that there may exist different elements with absolutely identical chemical character. Sir William Crookes, it is true, once thought, though the idea has not survived more extended examination, that the properties of the elements, as we know them, might be a mean value, and that the individual atoms composing the element might differ in weight and chemical character continuously on either side of this mean. If so, more refined methods might serve to resolve the element into a collection of what he termed "Meta-Elements," possessing the main character of the original, but differing from one another to a slight extent. Misled by the phosphorescence spectra, which are now known to be characteristic of mixtures rather than chemically homogeneous substances, he thought at one time that he had been successful in resolving yttrium. But the present idea that elements may exist, absolutely the same in chemical nature and yet absolutely different in other properties, such as radioactivity and atomic weight, is totally distinct from this. THE EXPERIMENTAL METHOD THAT FIRST REVEALED ISOTOPES. new I venture to think that no more elegant extension of our methods of gaining new knowledge has ever been obtained than that which, in due course, was to reveal the existence of isotopes. The original observations, upon which the theory of atomic disintegration was first founded, were that thorium is continuously producing a radioactive substance, thorium X, separable from it by precipitation with ammonia, but not with other precipitants, and, after separation, continuously re-forming again. The thorium X was short-lived, and changed again into a gas, the thorium emanation, for which the name thereon has recently been proposed, which was even shorter-lived and changed again to a solid, the "excited activ They In 1905, Sir William Ramsay and 0. Hahn were engaged in extracting radium from thorianite, a new Ceylon mineral containing both uranium and thorium in important quantities. The radium was separated with the barium, and the chlor ides fractionated in the usual way. found a new radio-element to be present, and to be separated from the radium with the barium. It proved to be the direct parent of thorium X, and intermediate in the series between the latter and thorium, and they called it radiothorium. In spite of this easy and apparently straightforward separation, the experience of a number of chemists showed that something remained to be explained, for it was found to be diflicult to the verge of impossibility to separate radiothorium from thorium. Ramsay and Hahn had in fact "separated" isotopes in 1905, for radiothorium and thorium are isotopes. Yet further work has shown the two to be so alike that no separation by chemical means is possible! Then in 1907, along with the radium which had been separated from thorianite, Hahn discovered another new radio-element, mesothorium, the direct parent of radiothorium and intermediate between it and thorium. In the next year he showed that mesothorium consists of two successive products the first, the direct product of thorium, mesothorium 1, being practically rayless and generating a short-lived product, mesothorium 2, giving powerful B- and y rays. γ This resolved the mystery, and one cannot do better than to quote the words of McCoy and Ross (J. Amer. Chem. Soc., 1907, XXIX, 1709): "Our experiments strongly indicate that radiothorium is entirely inseparable from thorium by chemical processes. The isolation of radiothorium from thorianite and from pure thorium nitrate may have been accomplished by the separation of mesothorium, which in time changed spontaneously into radiothorium." Thus the radiothorium separated from the minerai thorianite by Ramsay and Hahn was not the radiothorium in the mineral, but that subsequently produced from the easily separated mesothorium, after it had been removed from the thoriura. If they had fractionated the radium-mesothorium-barium mixture at once they would not have discovered radiothorium. The lapse of time after the separation of the mesothorium is essential. Nowadays many non-separable radio-elements are, like radiothorium, "grown" from their separable parents. Thus radium D, an isotope of lead, is grown from the radium emanation (radon), although it cannot be separated from the mineral, which always contains lead in quantity. The first part of the thorium series now runs*: In this series thorium and radiothorium and mesothorium and thorium X are two pairs of isotopes If we represent the successive products by balls of different colours to indicate their chemical character, isotopes being of the same colour, chemical analysis will sort the balls into their different colours, and the lapse of time will cause some of the colours to change. The ball representing mesothorium will in time turn into that representing radiothorium, so that the latter, before indistinguishable from thorium, becomes known as a separate individual. THE ISOTOPES OF URANIUM. It will be noted that the method of separating isotopes depends upon their being alternate rather than successive in the series. If radiothorium had been the direct product of thorium, the two would *The periods shown in the second line are the periods of average life of the successive products. These are 1.443 times the period required for one-half of the element to change. never have been separated to this day. The changes of chemical character are, as we shall later see, intimately connected with the electric charges on the a- and B-particles expelled. For successive products to have the same character no rays, or at least no charged particles, must be expelled. It is always as well-and no subject illustrates the point better than that of isotopes-to reflect not only upon what our methods are able to reveal, but also upon what they cannot reveal. If At first it seemed as if uranium itself was a case of successive isotopes. Boltwood, in 1908, proved from his study of the relative activities of the successive products giving a-rays in minerals, that whereas all of them, except uranium, gave off only one a-particle per atom disintegrating, uranium gave off two. By direct observation with the scintillation method it was proved that the two a-particles from uranium are not simultaneously expelled, and later it was shown that they possess different velocities. the slower comes from uranium itself (uranium I), the period of which is known to be 6.10 years, the swifter must come froin the isotope (uranium II), and its period must be some three million years. This is an example of isotopes being revealed by difference of radioactive nature simply, though no other evidence of their separate existences is available. Owing to the long periods of the a-ray giving members of the earl ypart of the uranium series, it has been much more difficult to unravel than the thorium series. As a result of researches too numerous to detail, it has been concluded that the main series is almost entirely analogous to the thorium series, and |