Apparatus for Demonstrating Sensitiveness of Selenium to Light.
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BY

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showers of sparks, direct from the mineral Pitchblende, Radium, Polonium, Uranium, Thorium, or any radio-active substance, even a Welsbach mantle contains sufficient Thorium to excite the very sensitive screen of the Scintilloscope, which is far more sensitive than the Spinthariscope. The Scintilloscope rivals the most delicate Eléctroscope as a detector of Alpha rays.

The eye sees an inexhaustible shower of stars of white light, giving a very realistic idea of the ceaseless activity of these marvellous substances which are producing the terrific bombardment causing this beautiful display.

See NATURE, September 29, page 535.. Glew's Scintilloscope Superior Lens, with Extra-sensitive Pitchblende and Polonium Screens, giving brilliant effects, Complete, 7s. 6d., Post free, U.K. Foreign Postage extra, weight 2 ounces.

Pieces of Pitchblende mineral, ground flat and polished, with Sensitive Screen attached, for use in Scintilloscope or with any strong pocket magnifier, from 7s. 6d. each, according to size.

Radio-active supplies of every description, on Sale or Hire. Radium Bromide, 1,800,000 units on hire for lectures.

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AN EXAMPLE OF WHAT THE SYSTEM ACCOMPLISHES:One hundred 4 oz. bottles are arranged in one Sytam Bottle-Element occupying less than 1 sq. ft. of wall space, each bottle is instantly located, removed or replaced, and any size from oz. to a Winchester can be accommodated in one and the same element.

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he says, "I have always thought that there must have been a formative epoch, in which every creature had the power of special adaptation to its own needs-nay even to its own wishes or caprice. In this epoch of 'plasmation' when the so-called force of heredity which tends to reproduction according to the type of the progenitor-had but little power, the world being still young, the organism must have been far more susceptible of modification by external forces (p. 36). . . . The actual power of adaptation in organisms is at the present day well nigh non-existent as compared with what they must have possessed in the past (p. 211). . . The varied forms assumed by those groups of individuals called by naturalists species, would be merely the result of a plasmative force exerted by surrounding conditions on primitive beings (p. 208). ... May it not be that the Rafflesia, and a host of other aberrant species, both animals and plants, are examples of the autocreation of organisms (derived from exceptional circumstances of the environment) and suddenly appeared à l'improviste, as it were, in that primitive epoch during which organic matter was easily plasmated, so as to adapt itself with facility even to extraordinary conditions of existence? (p. 389). . . . Therefore, contrary to the present prevailing tendency to attribute a powerful action to variability during the existing period, and to consider every species as inconstant, I hold the opposite opinion, namely, that at the present time species do not vary in Nature, returning thus to the old idea of the nearly absolute fixity of existing species (p. 210)." It is interesting to compare these views with those arrived at by Alfred Wallace, who wandered in the same jungles; and, as Dr. Guillemard, the English editor, rightly observes, "Whether the scientific reader does or does not admit the validity of all Dr. Beccari's theories concerning species-formation, he cannot call in question his abundant experience of the country, or his knowledge of the subjects of which he treats.'

OILS FOR MOTOR-CARS.

A. C. H.

POSSIBLY this article may be of interest to readers of NATURE who are not chemists, and therefore no apology need be made for treating certain parts of the subject in an elementary manner. The commercial names for motor-oils are numerous and confusing, and the automobilist may well be puzzled to discriminate between them, even if his chemistry has by no means become a mere schoolboy reminiscence.

The various liquids in use at the present time as fuels for motors are derived from three sources, namely, rrude petroleum, coal tar, and alcohols. By far the largest quantity is furnished by the petroleum. Coaltar "spirit" is scarcely beyond the experimental stage. Alcohol is somewhat largely used abroad, but at present is almost out of the question in this country.

Products from Crude Petroleum.-These, so far as motor fuel is concerned, are two: a light oil and a heavier or "burning" oil. The light oil, in one grade or another, is variously known as gasoline, petroleum spirit, petrol, petrol spirit, motor spirit, mineral spirit, motol, moto-essence, naphtha, petroleum-benzine, and benzoline. Of these, gasoline has the lowest density, benzoline the highest. The oil is obtained in the distillation of American crude petroleum, and may be said generally to be the portion of the distillate passing through the still between the temperature-limits of 60° C. and 150o C., and having a specific gravity ranging from 0.68 to 0.74. The limits, however, vary somewhat with the different refineries. To obtain a good motor "spirit" this fraction of the distillate is purified with sulphuric acid and with soda, and rectified.

by re-distillation. Such a spirit is clear, has no strong odour, and leaves no residue when evaporated from the hand. Two or three years ago the best English petrol had a specific gravity of 0.680; but, for reasons to be mentioned later, the density has been gradually raised, and is now generally about 0.720 or more.

Chemically, light oil or petrol is a mixture of several members of the homologous series of paraffin hydrocarbons, CnH2n+2 It is generally assumed to be mainly heptane, C,H,,, and octane, C.H,,, but both lower and higher members are usually present, and some analyses indicate that the range may commonly be from hexane, C.H,,, to undecane, C,,H, A point to notice is that whilst petrol as a whole is a light, volatile oil, it is by no means a homogeneous liquid. The different hydrocarbons composing it have not the same volatility as one another, and they require different quantities of air for their complete combustion.

24

The heavier oil obtained from crude petroleum corresponds to what is ordinarily known as kerosene, petroleum oil, or paraffin. It is obtained by refining the fraction which distils between 150° and 200°, and has a density of about 0.78 to 0.81. This product contains higher members of the paraffin series than those of petrol. It is consequently less volatile, and has a higher flash-point.

Kerosene is not only cheaper than petrol, but safer in the handling. Why, then, is petrol used so largely as a motor fuel instead of kerosene? And why are some kinds of petrol better than others? To answer these questions we have to remember that, to form the proper explosive mixture for the engine, it is necessary to have the vapour of the liquid mixed with a particular proportion of air. With too little air the mixture burns too gently; with too much there is a diluent effect. and liability to failure of ignition. The ready volatility of petrol allows of the requisite mixture being made more easily, more certainly, and with a simpler form of carburetter than when kerosene is used. Failure to ignite is less frequent, and the combustion is cleaner.

Nevertheless, since the supply of petrol is not limitless, attempts are being made, with some success, to utilise kerosene as a source of motor energy. The principle employed is that of heating up the vapour of the kerosene, or the liquid itself, in order to allow of a readier admixture with the air in the carburetter. This is effected either by the heat of the exhaust or by some other special contrivance. A "smokeless petroleum engine" has recently been described which is said to run without smoke or smell, and without "sooting" the cylinder. It will not, however, start with the cold kerosene. Petrol is used for the first revolutions in order to heat the vaporiser and raise the kerosene to the necessary temperature.

As regards differences of quality met with in motor spirits (petrol), the first thing to notice is that the higher the density of the liquid the nearer does it approach to the character of kerosene and to the possession of the disadvantages peculiar to the latter. To meet the growing demand, makers have been itere and more inclined to eke out their supply of petrol by including a portion of the heavier fractions that were formerly rejected. Hence many of the present oils are to that extent of inferior quality. Next, the density alone is not an infallible criterion, because a spirit having a density of, let us say, 0.700, may be made up in different ways. Ideally, it might consist of a single hydrocarbon having the density in question. On the other hand, it might be compounded of two hydrocarbons having widely different densities, such as 0.660 and 0.740 respectively. In the first case it would distil completely at one uniform temperature, in the second there would be a difference of perhaps a hundred