Page images
PDF
EPUB

slit. G is the "gitterplatte." P is a prism of 45°, with its refracting edge horizontal, and so placed as to bend upward the pencil of rays from G. T is the observing telescope, with the eye end elevated at an angle of about 35° so as to receive the rays from G after they pass the prism.

The spectra of the higher orders so overlap, that without the prism, or some analogous contrivance, it is impossible to observe in them any but a few of the strongest lines. By the prism these spectra are separated, one lying above the other; the red of the 6th order, for instance, falling below the yellow of the 7th, and this underneath the green of the 8th, while above this green lies the blue of the 9th order, and above that the extreme violet of the 10th. Thus the different spectra no longer interfere, and it is just as easy to observe the spectrum of the 8th order as that of the 1st, except that the former is fainter on account of the greater dispersion, and the obliquity of the grating, which narrows the transmitted pencil. A direct-vision prism in the eye-piece of the telescope answers the same purpose, but less perfectly. The same plan may have been used before. If so, however, I am not aware of it.

Hanover, N. H., April 19, 1876.

ART. LV.-Contributions from the Sheffield Laboratory of Yale College. No. XL.-On a Lithia-bearing variety of Biotite; by GEORGE W. HAWES.

THE feldspar quarries about Portland and Middletown in Connecticut have furnished many interesting minerals. The quarries are in the large granitic veins which intersect the gneiss and mica schist of the region. These veins, which have been described by various authors, are remarkable for the similarity of their mineral constituents, and the presence in several of rare elements, and it will be shown in this article that a lithia-bearing biotite is generally present. The feldspar is of two kinds, orthoclase and albite; considerable quartz is found, and with the feldspar it often forms beautiful specimens of graphic granite. Tourmaline, beryl, garnet, columbite, muscovite and biotite are common, and other species are found more rarely. Plates of muscovite and biotite united by their edges are of frequent occurrence, and sometimes one forms the center of a large crystal or plate of the other. The cleavage lines which are developed by striking the thin plates with a sharp point show that when the two species are thus united, there is a simple relationship between the axes of the muscovite and biotite, as long since found by Prof. G. Rose to be a general fact in the

case of such combined crystals of mica. Some of the specimens examined by Rose came from granitic veins similar to those of Portland and Middletown. The cleavage lines begun in one. mica often run some distance into the other without a change of direction, proving the complete continuity of the two.

The biotite of Portland is black, and possesses a high luster. In thin plates it is transparent, clear, and brown by transmitted light. It is optically uniaxial. Specific gravity 2.96. When heated before the blowpipe it imparts to the flame the characteristic carmine-red color of lithia, and it appears thus to differ from all the described varieties of the species. It afforded me, on analysis, the following results:

[blocks in formation]

The ratio of the R: R: Si is 1:1:2; and the analysis hence shows that the mica is an iron biotite, which has lithia replacing part of the potash, and which contains much more ferrous oxide and less magnesia than is common. It fuses before the blowpipe to a magnetic globule. Some specimens fuse with greater difficulty and give little color to the flame, indicating a transition toward the more ordinary variety. I would call attention to the fact that the iron of this mica oxidizes with great readiness both when heated and when exposed to the weather, and this shows how easy it would be to derive lepidomelane from it by alteration. This lithia-biotite seems to be widely distributed in granitic veins. Specimens from similar granitic veins in New Hampshire, Massachusetts and North Carolina were examined which imparted more or less of the lithia coloration to the flame, fused to magnetic globules, and which possessed the same physical appearance and the same association as the Portland biotite.

ART. LVI.-Researches on the Solid Carbon Compounds in Meteorites; by J. LAWRENCE SMITH, Louisville, Ky.

[Concluded from page 395.]

Action of strong nitric acid on the graphite.-Strong nitric acid, poured upon the powdered graphite that had been treated with ether and bi-sulphide of carbon acted vigorously upon the sulphide of iron mixed with it, and after digestion for some time in the acid and washing thoroughly with water, there remained 55 p. c. of the original matter, which consisted of carbon. This burnt in air with great difficulty, but very easily in oxygen, leaving a residue of one per cent of ash.

The nitric acid solution was analyzed and found to contain

[blocks in formation]

It is a fact of some interest that in the sulphide of iron which occurs in meteoric irons (when these nodules are perfectly free from any adhering iron) the quantity of nickel and cobalt present is very minute, a most singular fact if we are to regard these nodules as the result of segregations from the mass of iron. And still further, while the nickel is very largly the predominant metal of the two in the iron, I have noted that the cobalt predominates over the nickel in the sulphide nodules; but I would not without further examination regard this as likely to be the rule in all cases.

Action of fuming nitric acid mixed with potash chlorate on the meteoric graphite.-The oxidation of graphite by this method is well known to chemists, it having been first pointed out, as I have stated, by Mr. Brodie in 1860, and subsequently by Berthelot in his elaborate memoirs published in the Annales de Chemie et de Physique, 4th series, volumes xix and xxx. The result is the formation of a substance which Brodie called graphitic acid and Berthelot graphitic oxide, although the compound invariably contains hydrogen as an essential element in its constitution. M. Berthelot made use of this reaction to study the different forms of carbon, finding that the results of the oxidation varied with the carbon from different sources, only those forms of carbon known as graphites proper furnishing the graphitic oxide. The same chemist studied this oxid

izing action upon the graphite from the Cranbourne meteoric iron, and also upon the carbon from the Orgueil meteorite, and found that, of the two, only the graphite from the meteoric iron gave rise to the oxide.

The study of this subject I have pushed further, and have oxidized the graphites from the Sevier County and the De Kalb County meteorites, and have also re-examined that of the Cranbourne iron-having been very liberally furnished with a specimen by my friend, Prof. Maskelvne, of the British Museum. The carbonaceous matter from the Orgueil meteorite has also been subjected by me to the same reaction.

In

The details of conducting the process were identically those proposed by M. Berthelot in the memoirs already referred to, viz: To free the powdered graphite from sulphide of iron by first treating it with strong nitric acid, washing it thoroughly on a filter, drying it and mixing it with five times its weight of potash chlorate, then adding this mixture little by little to suf ficient fuming nitric acid to moisten thoroughly the mass. making the mixture, I place the nitric acid in a capsule and the latter in a little water with a piece of ice, thus avoiding any risk of explosion. The mixture, after standing a few hours is transferred to a ballon d'assais, and gently heated in a water bath at a temperature from 50° to 60° C. for several days. The result of this action upon the graphites of the Sevier County and DeKalb County meteoric irons was the formation of graphitic oxide, with all the characteristics of that furnished to Berthelot by the graphite from the Cranbourne iron, as well as to myself from this last graphite.

The conversion of the meteoric graphite into the oxide is more rapid than that of any terrestrial graphite with which I have experimented. The graphite soon changes from black to green, and finally, after two or three applications of the oxidizing agent, to a perfectly white substance. This, when filtered, washed, and dried under a bell glass with sulphuric acid, gives a yellow powder, somewhat adherent. If the oxidizing action of the nitric acid and potash chlorate be renewed several times on the same material, the oxide gradually diminishes in quantity, and if the process be stopped after the fourth or fifth treatment, the oxide is very gummy, adhering to the filter and preventing complete washing. When dried on the filter it adheres firmly, but can be detached by moistening the filter and rubbing off the paper with the finger, leaving tenacious flaky films.

The reaction and decomposition of the oxide obtained from the Sevier graphite is the same as that of the oxide from other

sources.

My experiments on terrestrial graphites have been confined

to the Siberian, Cumberland, and Ceylon varieties; and they show that the graphite under consideration differs from them in being more readily converted into oxide, it requiring only one-fifth to one-third of the time; and if the operation be continued by frequently renewing the oxidizing agents, the oxide first formed gradually diminishes in quantity, being more thoroughly altered, like some of those forms of carbon ranked as not properly graphites.

In fact, it appears that the meteoric graphites, when tested by this process, occupy a place between graphites proper and ordinary carbon, but much nearer to the graphites.

After completing my examination of the carbon nodules of the irons, my aim was to see what general deductions could be made with reference to the relations this graphitic material bore to the carbon found in the black meteoric stones. The material to operate with is, however, very rare; but I had in my collection enough for all necessary comparisons, though needing much more in order to obtain the peculiar products in sufficient quantities for chemical analysis.

The Alais meteorite.

Two grams of this meteorite were pulverized finely and treated with boiling water, which dissolved out a small amount of matter; which substance has been studied by others and it is not my object to recur to here.

The powder was then dried and treated with pure ether, in the same manner as the graphite from the Sevier iron, and the ether allowed to evaporate slowly at a moderate temperature, when the sides of the vessel became covered with acicular crystals, mixed with a few rhomboidal crystals. The residue had a peculiar odor, similar to that of the ether extract from the graphite of the Sevier iron, which odor it nearly lost in the same way, after several days exposure to the air. The form and appearance of the crystals are the same as of those obtained from that graphite; and a portion of the crystals detached and heated in a small tube gave the same character or reaction.

These crystals have already been studied by Prof. Roscoe, of Manchester, as carefully as could be done with the minute quantity at his disposal. My examination is perfectly in accordance with his, and there is no doubt that this product and that from the graphite must be of the same nature.

We must not forget to mention that Prof. Wöhler was the first to call attention to the hydrocarbon in these black meteorites when examining the one which fell at Kaba.

Orgueil meteorite.

This meteorite is one of the most interesting of all the known carbonaceous meteorites. And there are one or

« EelmineJätka »