researches I proposed to myself to take up this chance observation at another time, when I learned by a number of Dingler's Polytechnic Journal for 1849 that the fact had also been observed by Mr. Rochleder. The subject having thus lost for me its special interest, I published it without making any claims of priority.

"Since then, this observation has been taken up by Mr. Gaumond, who, by mixing the chlorid of sulphur with the sulphuret of carbon has made of it several interesting applications. He forms a soft elastic paste, with which he prepares the ink-rollers of printing presses. This was

in 1852."

At the same session, Mr. Balard communicated the results obtained in his laboratory by a workman, Mr. Perra, temporarily engaged there; this was in 1853. The following are some of the results:

100 parts of linseed oil with 15 to 20 p. c. of chlorid of sulphur gave an elastic product. With 5 p. c. of the chlorid the oil was thickened strongly without hardening; in this state it is soluble in all liquids which dissolve the oils, which is not true of the other products obtained with the chlorid. On mixing a given weight of linseed oil with thirty to forty times its weight of sulphuret of carbon, and then introducing one-fourth of chlorid of sulphur, the product remains liquid for several days. On applying this liquid to glass, wood, or any other solid body, the sulphuret of carbon evaporates immediately and the solid body is found to be covered with a varnish.

The chlorid saturated with sulphur is preferable to the pure chlorid. To succeed in these mixtures, it is necessary to put the chlorid quickly into the oil, and agitate it, in order to obtain a uniform product. By degrees it becomes heated; the oil hardens more or less according to the proportions of the chlorid of sulphur. It is necessary to operate with only small amounts of chlorid and avoid the elevation of the temperature. When the mixture is perfect, the material is thrown on a polished surface, as a plate of glass: after some minutes, it is done. A corner of the pellicle is detached with the point of a knife and immediately the whole is easily removed. Several layers may be added to one another, moisture being avoided at the moment of the operation.

Mr. Perra has in this way made small boxes and the handles of knives. By inserting a metallic cloth between two plates of this hardened oil, he has obtained plates that were quite durable. With some precautions, the plates may be made transparent and unalterable in the air; for this end, it is only needed to place them in a stove in order to expel the excess of chlorid. Cold renders the products hard and brittle.

Mr. Perra has not succeeded in making a substance analogous to hardened caoutchouc. He has colored the material or veined it like marble; and for this purpose the coloring material is mixed with the oil before the chlorid is added.

These products made from vulcanized oil are inconvenient for use, as they retain for a long time a disagreeable odor. They are not acted upon by dilute acids or alkalies. In the concentrated state, the alkalies sapo

* On the cause of the variation of angles in crystals, and on the isomorphism of homologous compounds. See Comp. Rend. Acad., 1848, and Comp. Rend. Trav. Ch, de Laurent et Gerhardt, 1849.

rify them. At 120° C. they become brown, and at a higher temperature they melt with a black color. For moulding, the material is excellent. It is in a high degree electric, and may be used for making electrical plates or the electrophorus. It readily destroys any tissues to which it may be applied.

Bromid of sulphur has properties analogous to those of the chlorid. Photochemical experiments. We have more than once had occasion to speak of Niepce de St. Victor, of the military ranks, who employs his leisure in the useful arts. If it shall be demonstrated that there is a fluid analogous to that of caloric and light, presiding especially over chemical phenomena, Niepce de St. Victor will have had a prominent part in the discovery. But a few months since, he ascertained the fundamental fact that a body which had been exposed to solar radiation could act in the dark at a distance on certain bodies, like light which emanated directly from the sun. The observations were made mostly with a cylinder of white pasteboard. Mr. Niepce has just noticed that the pasteboard that has been exposed to the sun, and then has been preserved in the dark in a cylinder of sheet tin (tinned iron), is still active six months afterward. This action of the chemical fluid calls to mind radiant heat.

Nitrate of uranium has in a high degree the property of magazining the chemical fluid. On exposing to the sun, under a photographic proof, paper impregnated with nitrate of uranium, and then at the end of a quarter of an hour, plunging it into a solution of nitrate of silver in the dark, a positive image immediately appears having the usual maroon tint. To fix it, it is only necessary to wash it with pure water. nitrate of silver is replaced by chlorid of gold, the image appears of a deep blue. These pictures resist the action of the cyanid of potassium, even on ebullition; they are therefore far more stable than photographs taken in the ordinary way.

If the

Tartaric acid has this same property, although in a less degree. Heat increases the sensibility of the reaction. For on covering with a plate of iron heated to 50° C. both the pasteboard which bears the impression from the sun and the leaf of sensitive paper prepared with chlorid of silver, the image will appear at the end of a few minutes, while at 0° C. it requires several hours to obtain a faint impression.

One general result of the researches of Mr. Niepce is this, that the bodies which preserve the greatest activity with a dose of the sun are, with the exception of the salts of uranium, those which are the least disposed to fluorescence.

This chemical activity which certain bodies may contract under the influence of the sun's rays or insolation, is greater or less according to the nature of the substance; it has its limits; when a substance has reached its maximum of activity continued exposure does not add anything to it.

Paper prepared with the nitrate of uranium changes color in the light and becomes insoluble; in the dark it is decolorized, and it becomes soluble after some hours, to be colored again in the light. It reduces the salts of gold and silver, so much as to become colored and insoluble.

A body rendered active by the sun will transmit this activity by contact in the dark to another body-tartaric acid, for example.

Mr. Niepce proposes to investigate whether the permanent activity communicated to a body by the solar rays is capable of determining the combination of chlorine and hydrogen, and whether it can be acquired in a luminous vacuum. An engraving wet and subjected to the sun reproduces itself on sensitive paper. But if it is covered with some millimeters of water, the effect fails, even with a solution of a salt of uranium or tartaric acid.

After having shown that certain bodies acquire by exposure to the sun, the property of reducing in the dark, salts of gold and silver, Mr. Niepce observes further that the reduction does not take place without the intervention of an organic substance. Paper is very good for this purpose, while no action is obtained if we take, for example the edge of a porcelain plate which has just been broken; on impregnating this edge with a solution of nitrate of uranium, no effect is obtained in the sun; but there is an action if we put on the edge a solution of nitrate of silver, containing a little starch or gum, and then sulphate of iron or gallic acid; a coloration is seen in the part subjected to the sun; it is the same if silver be used in place of uranium.

The reagents which Mr. Niepce employs by preference for demonstrating this action of the light are the salts of gold and silver, tinctures of litmus and turmeric, iodid of potassium for paper prepared with starch. In many substances that have been exposed to the sun the activity communicated is apparent in the insolubility; it is on a similar principle acquired under the sun's action by gelatine containing bichromate of potash, that Mr. Talbot has founded his photoglyphy. Heat and humidity promptly cause the loss of this property.

Mr. Niepce cites many examples in which the same results are obtained on inverting the course of operations; thus, a leaf of paper impregnated with gallic acid and exposed to the sun, treated by iodid of potassium, gives a feeble image which becomes very decided if subjected to nitrate of silver. A sheet of paper impregnated with chlorid of mercury and exposed to the sun gives an image with chlorid of tin, chlorid of sodium, soda, potash, and sulphuret of sodium. In the same manner a sheet impregnated with chlorid of tin, and exposed to the sun, gives an image with sulphuret of sodium, chlorid of mercury, chlorid of gold (Cl3 Au3) and nitrate of silver. A multitude of important facts are still to be drawn from the recent works of Mr. Niepce and we shall return to them again.

Reproduction of engravings by means of Phosphorus.-The engraving is exposed to the vapors of phosphorus burning slowly in the air; the black parts alone become impregnated with the vapors; it is then applied to a sheet of sensitive paper prepared with chlorid of silver; after a quarter of an hour of contact, the engraving is represented on the paper by a design formed of phosphuret of silver, which when it is sufficiently decided, resists the action of dilute chemical agents.

The best way of operating consists in placing the engraving in a box in front of a piece of pasteboard whose surface has been rubbed with a stick of phosphorus, and which covers one of the sides of the box. It is necessary to rub the pasteboard with phosphorus at each operation, because if the phosphorus becomes red phosphorus, it produces no effect.

Chemical nomenclature; making of new words.-To French men of science, or at least to those who seek to discover facts and new substances or species, it is a subject of gratulation that a French-and-Greek dictionary has recently been published. This dictionary is issued by the publishing house of Hachette. Its authors are three Greek scholars, of the highest merit, Messrs. Alexandre, Inspector general of the University, Planche and Defauconpret, Professors. There is also a complementary work-a Græco-French Dictionary by Mr. Alexandre alone.

Bibliography-At MALLET-BACHELIER'S, Quai des Augustin, Paris. Traité d'Optique physique, par M. BILLET, Prof. in the Faculty of Sciences at Dijon, tome I.-This work is altogether mathematical, and one of the kind has long been needed in France. Prof. Billet, with whom the higher optics is a specialty, has here published the results of 20 years of labor. The volume has already gone into the hands of all opticians and professors of physics.

Cours de Physique de l'Ecole Polytechnique, par M. JAMIN. Tome I, with 270 figures and a steel plate.-Mr. Jamin is Professor in the Ecole Polytechnique, and in this work he presents the programme of the course of physics in this celebrated school. From the range of the work it might well be entitled a General Treatise on Physics, for not only are the different topics profoundly treated, but also experimental demonstrations come to the aid of the theoretical and mathematical.

At HACHETTE'S, Rue Pierre Sarazin, Paris.

Résistance des Matériaux, 1 vol. in 8vo., 2d ed.-The first edition of this work appeared in 1853, and has been rapidly exhausted. Before preparing the second, its author, General MORIN, Director of the Conservatory of Arts and Trades, desired to verify by experiment the principal theories, and to this end has made many trials to test the accuracy of the hypotheses admitted in the ordinary theory with regard to the resistance of solids to flexure. He has also experimented on the resistance of sandstone to pressure, on which subject he gives an abstract of the trials made by the French engineer, Mr. Michelot, on the resistance of stones employed for construction at Paris.

Précis d'Agriculture théorique et pratique, par MM. PAYEN and RICHARD. 2 vols. in 8vo.-Among its topics, this work reviews the most recent discoveries on the principal points in the culture of land, besides being an elementary treatise on all departments of agriculture and even Zootechny, a science in which M. Richard is authority, as we had occasion to remark when announcing his "Dictionnaire raisonné d'Agriculture."

Problèmes de Mathématiques et de Physique, par M. MENU DE St. MESMIN. 1 vol. in 8vo.-This is a volume of exercises prepared with reference to students in the Department of Engineering including Mines, Bridges, Roads, etc. The problems are followed with solutions and explanations, and are illustrated by many figures in the text.

Dictionaire Grec-Français, et Français-Grec. 2 vols., grands in 8vo.This work is noticed above.

Dictionnaire des Cotemporains, par M. VAPPEREAU, grand in 4o de 1800 pages en 2 colonnes. In this work, the author proposes to give a biographical notice of the most distinguished cotemporary men in all de

partments of science, art, industry, literature, politics, and even war. This colossal work remains in the 'state of composition' from the beginning to the end, and therefore open to emendations, until the moment of publication. Supplements will be published as may be required. The whole dictionary is so put together as to admit of modifications, which must be numerous; for the good faith of the author has been more than once surprised.

This dictionary is not addressed only to the French, for men of all lands have a place in it; and the American reader will find a biographical notice of the principal men of the State, Art, Literature and Science in the United States.

Les Philosophes Français au 19e siècle, par TAINE, in 12-de 368 pages. -This work is written with much spirit, and in a style both elegant and well adapted in our view for the scientific criticism it contains.

DESCLOZIÈRES.-Vie et Inventions de Philippe de Girard, broch. in 12mo, avec figures.-Philippe de Girard was the inventor of the machine for spinning linen thread, and the author of many other inventions, well exhibited and appreciated in this small work.

SCIENTIFIC INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. On intermitting fluorescence.-J. MÜLLER has observed in platinocyanid of barium a peculiar phenomenon to which he has given the name of intermitting fluorescence. When a strip of paper is washed with a solution of the salt in such a manner that on evaporation the surface appears covered with a layer of delicate green crystals and then exposed in a dark room to the spectrum produced by a flint glass prism aided by a lens of long focal distance, almost the whole portion on which the blue rays fall appears blue. In this blue portion however, three isolated green fluorescent bands appear. The middle of one of these bands corresponds to Frauenhofer's line G; the two others lie between G and F. The centres of these bands correspond to the wave lengths 0.000462mm, 0.000446mm, 0.00430mm. From this it appears that rays of these wavelengths produce fluorescence, while those of intermediate wave-lengths produce none. An uninterrupted green fluorescence begins at that portion of the spectrum which corresponds to a wave-length of about 0.000410mm. No similar phenomenon has hitherto been observed.-Pogg. Ann., civ, 649.

2. On the increase in the resistance to electrical conduction which depends on temperature.-CLAUSIUS has pointed out a remarkable result deducible from the experiments of Arndtsen on the resistance of metals at different temperatures. Arndtsen had arrived at the result that in the simple metals, with the exception of iron, the resistance increases uniformly with the temperature and that in the different metals the comparative increase is nearly the same. Clausius remarks that Arndtsen's numerical results may be expressed by the formula

w1=w。 (1+0·00366, t),

in which w, is the resistance at the temperature t, w, the resistance at

1