« ÎnapoiContinuați »
of a great variety of very interesting compounds, and it yields, as before stated, mellilotic acid, which in its turn yields coumarin. It is mellilotol, and not coumarin, which is the cause of the odor of new-mown hay and of that of the flowers of the Mellilotus.-1 A, July 16, 25.
MANUFACTURE OF ARTIFICIAL VANILLA, It is not long since Messrs. Tiemann and Haarmann, students of Dr. Hofmann, of Berlin, made the discovery that vanillin, or the aromatic principle of the vanilla bean, can be obtained from the sap of the pine. These gentlemen have now completed their operations for going into the manufacture of the article on a large scale, as they find that the sap of an ordinary tree will furnish vanillin of the value of $20, without in the least injuring the wood for timber. Dr. Hofmann, in communicating these facts to the Academy of Sciences of Paris, remarks that this is the second vegetable product manufactured by purely chemical methods.-12 A, September 24, 1874, 427.
HYDROGENIZED IRON. Cailletet states that in his experiments on the passage, at ordinary temperatures, of hydrogen through iron, he has found that on allowing sulphuric acid to act upon a plate of iron, the hydrogen is, in part, absorbed by the metal, and that, by employing a system formed of two plates of iron soldered side to side, he finds the tension of the gas which accumulates in the apparatus is equal to a column of mercury 0.35 millimeter high. As the result of his investigations into this combination of iron and hydrogen, he says that this iron gives up, under water or other liquid, numerous bubbles of a gas which is pure hydrogen. In the open air the galvanic iron loses only a part of the hydrogen which it has occluded. When a piece of hydrogenized iron is brought near a burning body the hydrogen is rapidly disengaged, and the metal is surrounded by a light-blue flame. When the iron has lost by heat the hydrogen which it contained, one can not restore that gas to it. Employing a piece of iron that had been so heated as a negative electrode, Professor Cailletet found that the water is decomposed and the hydrogen disengaged as usual in abundance;
but the hydrogen does not again become occluded in the iron plate. Hydrogenized iron can be easily pulverized, but after it has been heated it retains a certain ductility. Hydrogen, in associating itself with the iron, communicates to it considerable magnetic force, so that the presence of hydrogen in irou modifies greatly the magnetic properties of this metal.
MICROSCOPIC EXAMINATIONS OF THE PROCESS OF CRYSTAL
LIZATION. Professor Frazer, Jr., exhibited to the Academy of Natural Sciences of Philadelphia a combination of the polarizer, vertical lantern, and microscope, by means of which the manner in which different salts crystallize out of their solutions, together with the manner in which they affect polarized light, can be explained and illustrated. The light from a lime lantern is passed through a rubber tube polarizer, then upward through the vertical lantern and a twoinch lens microscope, when it is again reflected horizontally on the screen. He explains that while this method has the advantage of so magnifying the crystals produced from small quantities of solutions that their structure can be minutely observed, as well as the sudden molecular change which causes the polarizing effect, it is open to the objection of a very large loss of light, first by the polarizer, and again by the microscope. A part of this difficulty, however, can be obviated by the use of the parabolic reflector.--Proc. Acad. Nat. Sci., Phil., 1875, 16,
A BRITTLE ALLOY OF IRON AND HYDROGEN.
Mr. Johnson communicates to Nature some important observations in reference to the action of hydrogen on iron and steel. Experiments made by him have shown that any acid which gives off hydrogen, when it is allowed to act upon iron or steel, produces the same effect, viz., of depriving the metal of its original toughness, and gives it the property of frothing when moistened with saliva. The gas coming off the surface of the iron, if cold, is shown to be hydrogen; and it seems probable that the brittleness of the metal is due to the occlusion of hydrogen within the iron. The simplest way of charging a piece of iron with hydrogen
is by laying it on a sheet of zinc in a basin of diluted sulphuric acid. The hydrogen generated by the action of the acid on the zinc is given off on the surface of the iron; and two minutes or less will suffice to charge a piece of iron with hydrogen, and alter its properties completely. This alteration is not confined to a diminution of toughness, which may be reduced to one quarter of its original value, but is also accompanied by a marked decrease in tensile strength, amounting in cast steel to upward of twenty per cent.; but in the case of iron-ware to only six per cent.
The electrical resistance is increased by this occlusion of hydrogen. It is probable that repeatedly rusting iron occludes hydrogen, and it is thereby deteriorated in strength and toughness.Nature, II., 903.
THE COMPOSITION OF BLEACHING-POWDER. The question of the composition of the so-called." chloride of lime” has lately been much agitated. The generally received view of Gay Lussac, that it is a true calcium hypochlorite, has been attacked by Goepner, who regards it as merely a molecular compound of lime and chlorine, containing no hypochlorous acid. Mr. Ferdinand Kopfer now submits the subject to the test of a long series of careful experiments, and decides in favor of the old view. He finds that when a dilute mineral acid, just sufficient to saturate the calcium present, is added to a solution of bleaching-powder, no smell of free chlorine can be detected, but only the characteristic odor of hypochlorous acid. The solution thus obtained, shaken up with a large excess of mercury, yields the brown oxychloride of the metal, again proving the presence of hypochlorous acid.—Jour. Chem. Soc., August, 1875.
THE INCOMPLETE COMBUSTION OF GASES. The habilitation thesis of Dr. Ernst Meyer on the incomplete combustion of gases contains the following suggestive sentences: The studies upon inflammability, which, according to the experiments contained in this essay, stand in a closer connection with the phenomena of affinity than we should at first suspect, indicate the importance that must be attributed to the thermal relations of the gases.
The combustion of carburetted hydrogen in a closed tube, which, beginning with the overleaping of the limits of inflammability, and with increasing quantities of oxygen, exhibits a series of different steps, until finally, by its total combustion, we reach an invariable final result, exhibits many interesting passages. Simple as is the result of the complete combustion, the incomplete combustion is exceedingly complex. If a mixture of carburetted hydrogen with oxygen approaches the limit of inflammability, then, in general, the steps of the combustion are exceedingly complicated. In this case the strong affinity of carbon for oxygen is shown, in that the latter at first serves exclusively to form carbonic oxide. When the hydrogen begins to take part in the burning, then there becomes evident, as we recognize from the compound nature of the resulting mixture of gases, an effort to establish an equilibrium according to the properties of the molecules. Similarly, under simpler conditions, in the case of the incomplete combustion of a mixture of carbonic oxide and hydrogen, the burning gases arrange themselves according to their molecules; and the same regularity holds in the complicated processes of the combustion of carburetted hydrogen, while in the latter the play of the affivities of carbon and hydrogen in general is easily recog. nized. Although we can not obtain clear views concerning their relative proportions, still the observations which are here given form definite starting-points for further considerations. These simplest processes will, perhaps, assist in the solution of problems of the highest importance in the mechanical explanation of the phenomena of chemical affinity. Precisely those conditions which variously affect the affinity of hydrogen and carbonic oxide, and which, as we may assume, may be referred to the different friction of the gases, point to causes which must be songht in the moving molecules themselves. A thorough study of such modifying circumstances will certainly advance our knowledge of the nature of chemical affinities.-Habilitations Schrift, Leipzig, 1874.
GASES OCCLUDED IN METEORITES.
within it there was a great predominance of the carbon compounds, which were plainly indicated by spectroscopic analysis; and by careful quantitative analysis it was found that 49 per cent. of the occluded gases were carbonic acid and carbonic oxide; the residue consisted largely of hydrogen. This meteorite is of the stony kind, in which the oxides of carbon are the characteristic constituents, while in the iron meteorites hydrogen is most abundant. The spectrum of the gases evolved from this meteorite, at a few millimeters' pressure, gave brilliant carbon bands; the brightest were the three in the green and blue, the red only being much feebler; agreeing in this respect remarkably with the spectrum of some of the comets, and affording a decided confirmation of the received theory as to the meteoric character of those bodies.-4 D, III., X., 44, July, 1875.
SOURCE OF THE ACID OF THE GASTRIC JUICE. The theories which have been proposed to account for the acidity of the gastric juice agree that this acidity is due to hydrochloric acid; but they differ as to the mode of its production. One theory supposes that the chlorides of the food are decomposed by the lactic acid which results from the decomposition of the carbohydrates ingested; the other that these chlorides are decomposed by simple dissociation. To test these theories, Maly has made a series of experiments, mainly upon dogs, but also upon the human subject. He confirms Bence Jones's observation that the acidity of the urine is diminished during the secretion of the gastric juice, being a minimum when the digestive process reaches its maximum activity. But as this fact may be accounted for on either theory-according to the first the lactates produced being oxidized to carbonates, and so entering the urine, and, accord. ing to the second, the dissociated alkali entering the urine directly-Maly sought to decide the question by ascertaining whether chlorides could be decomposed by lactic acid. Sodium chloride and lactic acid, when distilled, gave only at the last traces of hydrochloric acid. But diffusion experiments, in which lactic acid was mixed with sodium, calcium, magnesium, and ferrous chlorides, showed that hydrochloric acid was formed in dilute solutions. The question then recurred on the formation of lactic acid in the living stomach.