was discovered at the depth of 250 feet, amongst little blue and white topazes, hyacinths, zircons, tourmalines and stanniferous sands. The phosphoresence of hexagonal blende has recently claimed the attention of M. Edmond Becquerel. Although no really new fact has been discovered, a step has been taken towards establishing the relation existing between the solar phosphorescent rays and the other rays of the solar spectrum. We refer our readers to the original paper.* A Californian newspaper informs us that about three miles north of Ione in that country, there is an isolated mountain, which might be called a mountain of Agates, so thickly is it covered with those concretionary masses. They are described as being like large potatoes, generally of an oval, but sometimes of a globular form. When cut and polished, it is said they are of exceeding beauty. A communication has lately been made to the Academy of Sciences of Paris, on the remarkable Selenides which were discovered some six years since at Cacheuta, in the province of Mendoza, at the lower part of the Andes, and which have lately been examined by M. Domeyko. The seleniferous minerals appear to be of three varieties, in combination with silver, copper, and lead. The percentage of selenium varied between 22 4 and 30.8 per cent. METALLURGY. of The past quarter has been singularly barren of results in any the processes of smelting or preparing metals. The two following notes are the only ones, indeed, which even the scientific periodicals of Europe enable us to give. At the meeting of the Chemical Society, on February 7th, Dr. Matthiessen read an interesting communication on Alloys. Many of the examples given appear to promise to be of much practical utility. This paper has been more fully noticed in the report of the Proceedings of the Chemical Society. M. H. Caron has been making some interesting experiments on the Absorption of Hydrogen and Oxygen by Copper during fusion. Many of the results are of considerable interest; but as the investigation is incomplete, and as M. Caron promises to publish shortly the result of his experiments relative to the action of carburetted hydrogen and of carbon upon copper in fusion, we postpone our more detailed notice until the whole question is before us.f * See 'Les Mondes,' tome xii., p. 521. 11. PHYSICS. LIGHT.-Some experimental researches on the indices of refraction of saline solutions have been communicated by M. Le Verrier to the Academy of Sciences. His aim has been to ascertain whether the law, as laid down by Biot and Arago relative to gaseous mixtures, was equally true for liquids. Having experimented upon 153 solutions, he arrives at the following conclusions, giving at different temperatures for each body, its chemical composition, specific gravity, and index of refraction. The number representing the index of refraction varies according to the temperature. From 50° F. to 203° F. this variation often attains the hundredth part, and is greater in proportion as the liquid is the more concentrated. Its refringent power diminishes when the temperature is increased, and this diminution from 50° to 203° is about the thousandth part. The dispersion also diminishes with the temperature. In the same interval the distance between the two lines A and B of the spectrum may present a difference of a thousandth part. The law of Biot and Arago, that the index of a mixture of two gases is the mean between that of the two elements which constitute it, is therefore not strictly true in its application to liquid mixtures, but it may be regarded as a very close approximation, differing little from the truth, for a great number of saline solutions. When Nicol's prisms are used as polarizers or analyzers in delicate optical measurements, an anomaly is frequently remarked: the azimuths of extinction do not occur at a distance of 180°. The error can amount to several tens of minutes. This error would be fatal to the use of the Nicol's prism if the cause could not be discovered, diminished, and remedied. M. Cornu first pointed out this cause, and he has given the following explanation:-The axis of rotation of the prism, or rather that of the instrument which carries it, does not coincide with the plane of the principal section; hence the ray which traverses takes different directions in the prism according to the azimuth, and the polarization to which it is subject is not parallel to the plane of the optical symmetry of the crystal. When the lines of entry and emergence of the prism are quite parallel, it can be regulated by trial; in general the error will be only alternated and not annulled; but it may be eliminated in proceeding by crossed observations. In fact, it is easy to demonstrate by a very simple calculation and by direct observation, that the error e of the normal azimuth is given by the formula e = A (z + a) ; A and e being the contents; z the observed azimuth, it is easy to deduce that the mean of the readings of the azimuths, which should strictly differ by 180°, gives, after the subtraction of 90°, the real azimuth. The error is eliminated of its own accord, if we choose for the measurements of the azimuths the mean of two positions of extinction, whether for the analyzer or for the polarizer. M. E. Javal has described a new instrument which he calls the Iconoscope, intended to give relief to plane images examined with the two eyes. From the description we judge that this is an instrument similar to one which has long been known in England. It consists of an arrangement of prisms so placed that each eye receives an impression from the same point of view. On looking through the instrument at a picture, the eyes always preserving the same amount of convergence and being thereby unable to judge that the objects are on a flat surface, the painting has a semblance of relief. Mean HEAT. In the second part of a memoir "On the Changes of Temperature produced by the Mixture of Liquids of different Natures," recently published by Messrs. Bussy and Buignet, the following very important conclusions are arrived at:-1. In all the cases under examination, with one sole exception, the calorific capacity of the mixture is a little superior to the mean capacity of the elements. 2. By a singular opposition, the liquids for which the increase of bulk is the most considerable, are exactly those which develop most heat at the moment of their union, such as ether and chloroform, alcohol and water, sulphuric acid and water. while, the only instance hitherto noticed of diminution of bulk is the mixture of chloroform and sulphide of carbon, the decrease of temperature taking place at the moment of the union. 3. Independently of the loss of heat resulting from the changes of volume, there exists a cause which produces alone an absorption of heat an absorption which can be sometimes equal and even superior to the heat given out by the combination of the liquids. This cause, perhaps, may proceed from the separation of the homogeneous particles necessary for the diffusion of the liquids. M. Fizeau has continued his researches on the dilatation of crystals. He has experimented upon several series of salts presenting a great analogy with each other such as chlorides, bromides, and iodides-expecting that this analogy would be manifested by the manner in which crystals are influenced by the action of heat. His previsions are in general confirmed, and in the course of his studies he has discovered a singular anomaly, and one which constitutes a real discovery. While the coefficient of dilatation of all the chlorides, bromides, iodides, is positive, in the same manner as it is for all substances experimented upon up to the present day, the coefficient of dilatation of iodide of silver is alone negative, so that this salt, instead of dilating, really contracts. Raised to a temperature of 40° C., the coefficient is -0 00000139. This coefficient is besides variable with the temperature and the direction in the interior of the crystal. In the direction in which the contraction is greatest, parallel to the axis, it is the 750 part for 100° C., about a tenth of the dilatation of mercury. M. Matteucci has experimented on the adhesion of air to metallic surfaces. He heats plates of platinum in a current of oxygen or hydrogen; then he places them, while yet hot, in a closed apparatus containing one of the above-named bodies. Immediately there is a diminution of volume of the gases, and a formation of aqueous vapour by the combination of oxygen and hydrogen. It may happen that in the case of platinum the adhesion of the gases is not only to the metallic surface, but also in the interior of the metal itself. Metallic platinum is generally formed by hammering spongy platinum-a substance which has the property of exciting the combination of certain gases; hence it will not be unreasonable to believe that the molecular interstices opened by the heat would retain the gases, and thus cause their combination under the influence of other bodies in contact with them. Mr. Crookes has drawn attention to a curious result of the very severe frost experienced at the commencement of this year. Under the combined influence of cold and vibratory motion, large masses of glycerin were noticed to have assumed the solid crystalline state. About five tons of glycerin, in casks of eight cwt. each, were recently imported from Germany, by the firm of Burgoyne, Burbidges, and Squire. When they left the factory the contents were in their usual state of viscid fluidity; but on arriving in London, they were found to have solidified to a solid mass of crystals, so hard that it required a hammer and chisel to break it up. A large block of this solid glycerin, weighing several hundredweight, suspended in a somewhat warm room, took two or three days to liquify; and a thermometer inserted in the fusing mass indicated a constant temperature of 45° F. In small quantities, the crystals rapidly fuse when the bottle containing them is placed in warm water. In quantity the solid glycerin looks very like a mass of sugar-candy. The isolated crystals are sometims as large as a small pea; they are brilliant, and highly refracting; when rubbed between the fingers they are very hard, and they grate between the teeth. Their form appears to be octahedral. The crystals, separated as much as possible from the mother liquor, and then fused by heat, form a clear and nearly colourless liquid, slightly more viscid than usual, which possesses all the physical and chemical properties of pure glycer n. Some of the fused crystals have been exposed for several hours to a temperature of 0 F. without solidification taking place. The only result was that the liquid became more viscid. The cause of the crystallization is not very clear. The most probable explanation is, that the vibration of the railway journey across Germany, added to the intense cold to which the glycerin was simultaneously subjected, enabled the particles to arrange themselves in a regular form. The phenomenon then becomes analogous to the crystallization of wrought iron under the influence of vibration, and the gradual solidification of syrupy solutions of organic alkaloids. Mr. Skey, Analyst to the Geological Survey of New Zealand, has discovered the curious fact that if tungstic acid is made redhot, and then brought in contact with a cold surface, it assumes a black colour, which is permanent in the air. The change in colour here produced appears to be due to the presence of the oxide of tungsten. The effect of a sudden refrigeration of tungstic acid, therefore, is to deoxidize it. If the hot acid is dropped into kerosene oil, the same effects follow. M. Becquerel, in his name and that of his son, M. Edmund Becquerel, has presented to the French Academy a new series of observations, thermometric and hygrometric, taken simultaneously in free air and under trees, the general results of which may be summed up as follows:-In summer the mean temperature in free air slightly exceeds that under the trees; in winter the contrary is the case. The trees, in spite of their inferior conductibility, very slowly assume a temperature in equilibrium with that of the air. The diurnal maximum takes place towards midnight under the trees, whereas it occurs towards three o'clock in the afternoon in free air. A little more rain falls three kilometres from the wood than at its verge or in the interior. The climate under the trees is therefore a sort of sea-climate, and this conclusion of the thermometric and hygrometric observations is confirmed by numerous facts of vegetation. The Steam Ice-Machines of M. Toselli, are at present attracting some attention in Paris. An ice-producing machine capable of forming 22 lbs. of ice per hour, or nearly 2 cwts. per day, is a square parallelopiped 9 feet 2 inches long, 6 feet 3 inches wide, and 6 feet 5 inches high. It consumes nearly a halfpennyworth of charcoal for every kilogramme of ice formed, and only requires the attention of one man to set it at work and to give the necessary movement to the circulation of the water The machine costs 1807. We believe that the principle on which it is based is the rapid vaporization of a highly volatile liquid, the necessary supply of heat being taken from the water to be frozen. |