Sir William Crookes,
Pierre and Madame Curie

SIR WILLIAM CROOKS

William crookes was born in London in 1832. Lister was then five years old, William Thompson, aged eight, was playing with his brothers and sisters in the Belfast meadows, and Lyell was eagerly discussing with Miss Mary Horner the prospects of the Reform Bill.

In 1848 William Crookes entered the Royal College of Chemistry, as a pupil of Dr. Hofman, and it was here that he began his earliest scientific researches, publishing in the Quarterly Journal of the Chemical Society a paper On the Seleno-Cyanides  in 1851. From that time he was steadily engaged in the study of chemistry and physics, and three years later was appointed to superintend the meteorological department at the Radcliffe Observatory, Oxford; it was in 1861, when he had been six years Professor of Chemistry at the Chester Training College, that he isolated the new element, Thallium. Whilst holding the residue of the iron pyrites deposited in "the flues of a sulphuric acid chamber" in the flames of a Bunsen burner, he noticed a green line, to which he could not give a name. Traced to its source he found that this soft metal, almost white in colour, closely resembled lead in its physical properties. It tarnished quickly, volatilizing at a red heat, and occurred chiefly in copper and iron pyrites. In the same year, having discovered the new metal by means of spectroscopic analysis and chemical reactions, he produced a series of analytical notes on thallium, but his researches on its atomic weight were laid before the Royal Society only after eight years' laborious work.

In the meantime he had discovered a method, known as the sodium amalgamation process, for separating gold and silver from their ores, and, being already regarded as an authority on sanitary matters, he was appointed by the Government in 1866 to report upon the use of disinfectants in arresting the spread of the cattle plague. So varied had been his studies that five years later, as a member of the English expedition to Oran, in Algeria, Crookes was making reports neither on chemistry nor disease, but this time on the total phase of the solar eclipse occurring in December, 1871. He began next year to conduct experiments on "Repulsion resulting from Radiation", and as a Fellow of the Royal Society, published many papers on this and collateral subjects, his work being an "extension of experiments begun by others so long ago as 1790" or even earlier. At all events Faraday had experimented with vacuum tubes, and nearly two hundred years before Otto von Guericke had invented a workable air-pump. It was not till the mercury air-pump was used, however, producing a very high degree of exhaustion, that the disturbance of ether resulted which is now known as X-rays. At that time (1865) nobody suspected their existence; there was in consequence nobody to see them, till Roentgen, who wished to learn all that there was to learn about vacuum tubes, observed a mysterious shadow on his luminescent screen. Now, the tube was enclosed in thick black cardboard, but Roentgen, driven to the belief that the rays proceeded from it, investigated their power of penetrating wood, cloth, paper, and metal. Metal offered a certain amount of resistance; the other substances were of no more use to keep out these unknown invisible rays than glass to keep out sunlight. In short, the bones of the human skeleton could be viewed, by X-ray photography, through  the body, and Roentgen's preliminary discovery in 1895 aroused worldwide interest. It was Professor Henri Becquerel, however, who discovered what he and Sylvanus P. Thompson, investigating the same subject in London, thought to be the action of X-rays reversed; that is to say, X-rays produced fluorescence (or the blue luminous appearance of certain substances when exposed to sunlight), but could fluorescent salts, stimulated by the sunlight, produce X-rays? Uranium salts did, it was proved, give off radiations, markedly affecting the sensitive photographic plates; Becquerel presently discovered, however, that this action was due to something inherent in uranium, and was not the "converse" of X-rays. Some substances, of which uranium was one, were "radio-active", and one substance, which was clearly radio-active above all others (as we shall see later), was named Radium.

Crookes' work was an extension of the experiments of Faraday and others; on the other hand the work of Becquerel, and later of the Curies, was an extension of his  investigations, resulting, notably, in the invention of the Radiometer. This delicate instrument consists of four light vanes, suspended horizontally and radially, in a vacuum, and capable of freely rotating round a vertical axis. Each disk or vane has one side white, one black, and light or heat repels the blackened surface, so that in the dark the vanes are motionless, but when brought into the light they rotate in a definite direction. The blackened sides absorb the heat rays and increase in temperature; the molecules still present (a perfect vacuum being impossible) therefore rebound with greater velocity from each blackened surface than from the white, and the recoil forces the vanes round. This instrument showed many remarkable phenomena of "repulsion and attraction", and Crookes obtained, by his radiometer experiments, pressures as low as .00015 mm. or the 2 millionth of an atmosphere. He was thus led to his famous researches on phenomena produced by the discharge of electricity, through highly exhausted tubes (Crookes' tubes), so that in a very real sense his work made possible the discovery of Roentgen rays.

From 1883 onwards William Crookes was engaged in Radiant Matter researches, his "Radiant Matter" test being a method of spectroscopic examination which "seemed likely to throw a side-light on the origin and constitution of the elements", and he developed a theory, amongst many other important discoveries and investigations, that all the elements are derived from one primordial stuff, protyle. He received from the French Academie des Sciences, in 1880, a gold medal and a prize of 3,000 francs in recognition of his researches in Molecular Physics and Radiant Matter. He was knighted in 1897, made President of the British Association in the following year, and in 1906 celebrated his golden wedding.

In 1859, when William Crookes was Professor of Chemistry at Chester, Pierre Curie was born, the man who was to continue Henri Becquerel's work, and to discover Radium. He was educated at the Sorbonne, Paris, where he afterwards became Licencie es Sciences Physiques, and Docteur es Sciences, and from 1900 onwards held the chair of physics. His wife, Maire Sklodowska, was a Polish girl, who had come to study in Paris. When she married Pierre Curie, the two worked together, and it would be hard to say how much the world owes to their learning, imagination, and patience.

Two years after Becquerel discovered the radio-activity of uranium, the Curies found, by testing samples of pitchblende—the mineral from which uranium is obtained—that it was more radio-active even than the uranium salts. Their task was therefore to discover the substance in pitchblende besides uranium which was radio-active. They discovered, after careful analysis, that the waste rock from which uranium was extracted, contained a new element, which Madame Curie christened Polonium, after her native land. Further examination, however, ended in the isolation of a third substance more radio-active either than uranium or polonium, and this they called Radium. To the unscientific world, radium appeared to be a kind of Aladdin's lamp; there was no end to the miracles it was to work, especially as it was generally understood that the new substance would endure for ever, and that all the energy hitherto produced by steam-engines and other engines could be procured from one minute piece of radium. All diseases were to be cured, and man himself was to look to radium for the light and heat needed to keep him alive.

If radium possessed life-giving powers, however, it was nevertheless dangerous, and many investigators, including Professor Curie, suffered from painful ulcers on the hands due to the handling of this mysterious white powder. Animals exposed to radium lost fur, skin, and eyesight, and finally died; on the other hand, radium has healed diseases thought to be incurable: it is a good servant, a bad master.

Sir William Crookes, and other scientists all over the world, were devoting themselves to the study of radium and its radiations; having been long engaged in studying the nature of Radiant Matter—substances, that is to say, whose heat is due not to contact, but to the rays emitted—Crookes invented an instrument, known as the "Spinthariscope", devised to show the scintillations which are produced on a "blende" screen when a piece of radium nitrate is brought near it, a short brass tube, having at one end a blende screen with la speck of radium salt about a millimetre in front of it, and at the other end, a simple convex lens.

In the meantime prolonged and careful investigation brought to light the following facts. In the first place radium is exceedingly difficult to obtain. Pitchblende appears in the veins of gold, silver, and mica, chiefly in Bohemia; but thousands of tons must be refined to procure even a kilogramme of radium. In the second place, three different kinds of rays are emitted from radium, known as the alpha, beta  and gamma  rays. The alpha rays are "easily absorbed by metals, and are projected bodies, not waves. These bodies are about the size of a hydrogen atom, they are positively charged, and travel with about one-tenth of the velocity of light". The beta, or cathode rays, on the other hand, are negatively charged, more penetrative, and more easily deviated, and appear to consist of particles of about one-thousandth the mass of the hydrogen atom. The gamma  rays, closely resembling Roentgen rays, possess a very great power of penetration, but the alpha  radiation is by far the most important. "The determination of the mass of the alpha  body," wrote Professor Rutherford in an article in Nature, August 20, 1903, "taken in conjunction with the experiments on the production of helium by emanation, supports the view that the a particle is in reality helium." Now, helium was a gas discovered by Lockyer in the sun's atmosphere (hence helium, from Greek helios, sun), and believed at first to be an element existing only in the sun and stars. The "helium radiation" of radium was this mysterious gas, which had been thought lacking in our own planet, and according to Professor Rutherford, when an atom of radium breaks down, some of the electrons composing it are free, and become beta  rays, whilst the others become alpha  or helium rays.

The matter remaining after the a radiation has been thrown off condenses at low temperatures, and may deposit itself on bodies with which it comes into contact. That is to say, this "emanation" causes objects in its neighbourhood—from the cardboard box which may have contained radium tubes, to the experimenter's skin—to become radio-active; they are temporarily infected with the active principle of radium, and can disturb the working of delicate scientific instruments.

One surprise has followed another; and there was never a scientific discovery so sensational as the discovery of radium. Whence come these unknown radiations? This is the question which has yet to be answered, and that radium will throw light on many of the problems of electricity, and of life, seems highly probable. Pierre Curie was killed in 1906 by an accident, an irreparable loss; but Madame Curie continues the work they had begun together, and we are still very far from realizing to what discoveries the world will be led by radium, the "Miracle of Science".

M. AND MADAME CURIE.