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Rh ACHMANINOFF, SERGEI VASILIEVICH (1873-), Russian composer and pianist, was born at Onega, in Russia, March 20 1873; his grandfather, an excellent pianist, had been a pupil of the Irish musician John Field. He began his studies under his mother, but at nine he became a pupil of Anna Ornadtskaya. In 1882, however, the Rachmaninoff family removed to St. Petersburg, and Sergei entered the Conservatorium, where he remained till 1885, when, on the family again removing to Moscow, he joined the Conservatorium there, and was on terms of friendship with Scryabin, Siloti, Taneyeff and Arensky. When, in 1892, Rachmaninoff left the Conservatorium, he won the large gold medal for a one-act opera Aleka and followed it by many other works. About 1893 he composed a pianoforte suite, another for two pianos, a dozen songs, his first piano concerto, the symphonic picture The Rock and the elegiac trio on the death of Tschaikovsky. Next there followed his first symphony, produced by Glazounoff at St. Petersburg. In 1897-8 Rachmaninoff became conductor of Mamoutoff's private opera, a post he resigned after the season, and in 1899 he came to London to conduct a Royal Philharmonic concert. A second piano suite, another concerto and a violoncello sonata were quickly composed, and were followed by the one-act opera The Miser Knight (Moscow 1900, Boston 1910) and Francesca da Rimini (Moscow, same evening); during 1904-6 he directed the Moscow Opera, and from 1906 to 1908 he lived in Dresden as composer and pianist, visiting Paris in 1907. In 1909-10 he visited the United States for the first time, and then returned to Russia, where he wrote The Island of Death, the D minor piano Sonata, and the third and fourth piano concertos (1909 and 1917). In 1912 he produced The Bells, which was produced in Liverpool by Sir Henry J. Wood in 1921. Among his other compositions Spring, for chorus and orchestra, is particularly noteworthy, and his devotional music includes a wonderful setting of the Liturgy of St. Chrysostom (1910). In 1917 Rachmaninoff left Russia, and in 1918 he settled in New York.  RADIOACTIVITY (see 22.793*). Among points" of special interest that have arisen since the earlier article was written may be mentioned the preparation of metallic radium by Mme. Curie and Debierne by electrolysis of a radium salt with a mercury cathode. Radium resembles metallic barium, melts at about 700 C. and is rapidly attacked when exposed to the air.

The atomic weight of radium was found by Mme. Curie to be 226-45, using for the purpose about 0-4 gram of pure radium chloride. A recent careful redetermination by Honigschmid with about one gram of radium gave a value 225-9 an d is prob- ably correct to i in 1,000. An International Radium Standard consisting of about 22 milligrams of pure radium chloride has been prepared by Mme. Curie, and is preserved in the Bureau International des Poids et Mesures at Sevres, near Paris. Secondary radium standards have been issued to all governments who wished to purchase them. These have been calibrated by 7-ray methods both in Vienna and Paris and are supposed to be correct within i in 200. During the last few years the purchase and sale of radium have generally been conducted on certificates given in terms of this international standard.

The wide use of radium for therapeutic purposes, and its high cost from 25 to 30 per milligram element have led to close search for uranium deposits. The amount of radium in an old mineral is always proportional to its content of uranium in the ratio of 3-3 parts of radium by weight to 10 million parts of uranium. Consequently an old mineral containing 1,000 kgm. of uranium should contain 330 milligrams of pure radium. Initially several grams of radium were separated from the uraninite deposits in Joachimsthal, Bohemia, and some of the material, which was the property of the Austrian Government, was generously loaned to representative workers in radioactivity in England. A part of this radium is in the charge of the Radium

Institute of Vienna, which is specially devoted to radioactive investigations. The increasing demand for radium has led to the working of low-grade uranium ores on a large commercial scale. Much of the radium to-day is derived from the mineral carnotite, of which there are extensive deposits in Colorado and other parts of the United States. Although the carnotite contains only a few per cent of uranium and a correspondingly small quantity of radium, the separation of the latter is a profitable industry operating on a large scale. Large quantities of radium were employed by the Allies during the World War for night compasses, gun-sights, etc. The radium is mixed with phos- phorescent zinc sulphide to form a paint which becomes con- tinuously luminous, but, owing to the destruction of the zinc sulphide by the rays, this luminosity gradually decays.

Radium Emanation. The atomic weight of the radium em- anation is now known to be 226 4= 222, as was inferred earlier. This was confirmed by direct weighing with micro-balance by Ramsay and Gray.

The radium emanation has proved of great service not only in radioactive researches but also in therapeutic work. The radium salt is dissolved in an acid solution and the emanation is pumped off with the large quantity of hydrogen and oxygen liberated by the action of the radiations on water. After sparking the mixture, the emanation can be purified by condensation with liquid air. A very intense source of /3 and 7 radiation can be obtained by introducing the purified emanation into fine capillary tubes. Such emanation needles have been widely used for therapeutic purposes, while the use of very thin-walled tubes provides a powerful line source of a rays. The |8 and 7 activity of such tubes rises to a maximum about four hours after introduction of the emanation and then decays with the period of the emanation, viz. 3-85 days. The quantity of emana- tion liberated from one gram of radium is called a curie and from one milligram a millicurie. The quantity of radium emanation in a tube can be accurately determined by comparison of its 7-ray activity with that of a radium standard, since the penetrating 7 rays, both from the radium and the emanation in equilibrium, arise mainly from the same product radium C.

As regards other radioactive substances large quantities of meso- thorium have been obtained as a by-product in the separation of thorium from monazite sands. This substance, which is half trans- formed in about 6-7 years, emits only /3 rays, but gives rise to radio- thorium and subsequent products which emit a rays and penetrating /3 and y rays. As a source of powerful and 7 radiation, this sub- stance is very analogous to radium and can be obtained in about the same concentration. Since radium and mesothorium are isotopic elements, they are always separated together. Most commercial sources of thorium contain also uranium and radium, and con- sequently radium is always separated with the mesothorium and in relative amount depending upon the proportion of uranium to thorium in the mineral. Since mesothorium has a radioactive life short compared with radium, it commands a smaller price. The amount of mesothorium is standardized by comparison of its 7-ray effect with a radium standard.

Mme. Curie separated the polonium from several tons of pitch- blende and obtained an exceedingly active preparation of a few milli- grams, but was unable to obtain it in a pure state, although several of its spectrum lines were detected. It was hoped by this experiment to decide whether polonium was transformed directly into lead, but this was found difficult to establish owing to the presence of im- purities with the very small quantity of polonium.

The three types of radiation, known as the o, ft, 7 rays, emitted by radioactive substances are analogous in many respects to the types of radiation observed when a discharge passes through a vac- uum tube, but are of much more penetrating character. It may be noted here that for the electrons in a vacuum tube to obtain the velocity of the swift /3 rays from radium, a potential difference of at least two million volts would have to be applied. The very penetrat- ing 7 rays are identical in all respects with X rays of very short wave- length. Intense 7 rays are only observed in substances which emit swift ft particles, and apparently owe their origin to the passage of the swift /3 particle through the distribution of electrons surrounding the atomic nucleus. To produce X rays as penetrating as the 7 rays, about two million volts would have to be cut on the discharge tube.

The a rays, shown in 1903 by Rutherford to consist of a stream of positively charged atoms projected with high velocity, are now known to consist of charged atoms of helium which are projected with velocities of about 10,000 m. per second. While the majority of products break up with the expulsion either of an a particle or a swift /3 particle, in a few cases no detectable radiation has been observed. Such products were at first called " rayless " products, but the sequence of


 * These figures indicate the volume and page number of the previous article.