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considerable. According to M. Xardel some rare samples exist which afford even 45 (a) 50 per cent; * * * other specimens afford 20 (2) 25 per cent. The beds which are worked, or are capable of being worked, yield from 5 to 9 per cent.” [p. 675.]—Again [p. 676), “The impressions of fossils, so common in the shales of d'Igornay, occur in the poorer shales. The rich shales, on the contrary, often contain vegetable remains analagous to those commonly found in the coal measures. Perhaps the beds of rich shale are in a manner the representatives of coal-beds; it is to be remarked that in the shale which yields 9 per cent of oil its sheets are covered with a multitude of shining (miroirtantes), lenticular veins, having a waxy fracture, which by their aspect and manner of burning recall the variety of coal which is called cannel coal.” —Leaving it for our readers to answer the question; how far removed in anything but productiveness is the “coal” (Boghead) upon which Mr. Young has operated from the “shale” distilled by M. Selligue? . It may not be amiss to mention the fact that upon the continent of Europe the Boghead mineral is almost universally called, not coal, but shale. A fact with which the reader can readily enough familiarize himself by consulting the German chemical journals of the last eight or ten years. In proof of it we cite only the following:* “The recent verdict in the celebrated Torbanehill-mineral case appears to be contrary to the scientific opinions held in Germany, as proof of which we have a case in point, and which, although not at the time known in this country, was officially decided upon in Berlin previous to the trial coming on in Scotland, which terminated on the 4th of August last. It appears that in Frankfort-on-the-Main there has, for some time past, been in existence a company for lighting the streets and houses by gas from oil, resin, &c. A rival English company contracted to light with coal-gas; and to give both fair play, it was decided that the latter company should be confined to the use of coal alone. Mr. Engelhard, the manager of the Oil (Resin) Gas Company, having heard of the Boghead and Torbane mineral, obtained specimens, and having found they produced excellent gas, gave an order for a large consignment which reached Frankfort vid Rotterdam, through a Dutch agent. This was entered at the Custom-house as cannel coal, much to the annoyance of Mr. Engelhard, who was no more at liberty to make gas from coal than his rivals were to make it of anything else but coal. He was, however, prevented from the necessity of a trial at law, for the officials did not feel themselves justified in charging the duty as coal, although, as other mineral, it would pass free, and applied to higher authorities for instruction. These parties were as much at a loss as their inferiors, and the case was eventually transferred to the Central Board of Customs at Berlin, the last court of appeal of the Prussian Zollverein, where all disputed questions in the German States are settled. Scientific men, connected with the board, examined the Boghead and Torbane mineral and decided that it was not coal, but bituminous shale, which is said to be the general opinion among German chemists. It has been admitted into Germany, duty free, and Frankfort is now partially lighted with gas from this mineral, charged for as resin or oil gas. It is described as a clay containing bitumen, and producing oil when heated. At all events, we may take this German decision as impartial as, had it been admitted as cannel coal it would have been subject to a duty varying from 1s, to 1s. 6d. per ton.” In connection with the question of the products of the distillation of coal which Dr. A. would have us believe so entirely new to the world and to this country in particular, we cite the following from The Encyclopædia of Chemistry, by James C. Booth and Campbell Morfit. 8vo, Philadelphia, Baird, 1850, p. 461. Article, Coal: paragraph, “products of dry distillation.” ‘.

* See London Journal of Gas Lighting, Oct., 1853, iii, 256; from London Mining Jowrnal.

“These products [of the dry distillation of coal] are somewhat analogous to those derived from wood, and some are identical with them. * * * The liquid products consist of various bodies closely allied to petroleum, and the solids Naphthaline and Paraffine. The relative proportions of these products vary with the temperature. The lower the heat employed, the less gas, and the more solids and liquids are produced; the higher the temperature the greater is the quantity of carburetted hydrogen.” Before closing this sketch we must refer to and correct a palpable error of Reichenbach’s” which has been cited by Dr. Antisell (p. 14), from whom we quote it: “So remained paraffine until this hour [date of Y.'s patent], a beautiful item in the collection of chemical preparations; but it has never escaped from the rooms of the scientific man.” Upon the reader who has followed us thus far we need not urge that the above statement is incorrect. As an offset to it we cite the following: “In the Parisian Industrial Exhibition for 1839 Selligue exhibited: 1st— Bituminous shale, then fluid bitumen scrude oil], mineral grease, crude and refined (the former at 50 fr. the 100 kilog. [= $5.00 per 100 lbs.]), also mineral war [paraffine] crude and refined (the former at 125 fr., the latter at 180 fr. [= respectively 12} and 18 dollars per 100 lbs). The purified mineral wax was beautifully white but the candles made of it had a soiled appearance.” W. Hermann (now, according to Wagner, councillor of State in Munich goes) on to assert that “if these fatty products can be prepared economically they belong to the most important objects of the Exhibition.” It would be foreign to our purpose were we to attempt to trace the recent history of the art of manufacturing coal-oil, even if our space allowed of it. During the past few years a large number of paperst on the subject have been published in the Scientific Journals of Germany; while several recent works upon the materials used for producing light have each devoted a separate chapter to its description. A few special treatises have also been published of which the following is a, doubtless very incomplete, list.—$ UHLENHUTh, Ed. Handbuch der Photogen- und Paraffin-Fabrikation aws Torf, Braunkohle und bituminösem Schiefer nach den newesten Versuchen whd Erfahrungen. Quedlinburg, Basse, 1858. MUELLER, Carl, Georg, Die trockene Destillation und die hauptsächlichsten auf ihr beruhenden Industriezweige. Leipzig, Barth, 1858. DANckwort, MEITzENDoRFF und WERNEcKE. [Committee of the Magdeburg Gewerbeverein.] Ueber das Photogen oder JMineralal, so wie die ihm

* Erdmann's Journal für praktische Chemie, lxiii, 63. Did our space allow, we would gladly transcribe the whole of this article—an English translation of which may be found in the London, Edinburgh and Dublin Philosophical Magazine, [4] viii, 463—in proof of our assertion that the present widely-spread manufacture of coaloil and paraffine is mainly due to the comparatively recent discovery of rich stores of highly bituminous substances.

+ From v, Hermann's Die Industrie Ausstellung zu Paris im Jahre, 1839, Würn berg, 1840. p. 147;-in Wagner's Jahresbericht weber die Fortschritte der chemischen Technologie, 1855, i. 416.

+ Very complete synopses of these may be found in Wagner's Jahresbericht, four volumes of which have thus far been published. For references to the recent admirable scientific researches of GREVILLE WILLIAMs, DE LA RUE, and others, which have been chiefly confined however to the more volatile portions of the oil and to the basic compounds which occur in it, see Liebig and Kopp's Jahresbericht der Chemie, u. S. w.

§ Small as this list is, it will nevertheless recall to the mind of the reader the modest lines with which Dr. Antisell's preface commences, namely these: “the present little treatise is the first published monograph on the art of distilling oils from minerals containing Bitumen.”

dhnlichen Leuchistoffe, in Bezug auf ihre Feuergefährlichkeit und ihre Anwendung. Magdeburg, 1856. . e Also the insignificant brochure of ScHRADER, F. W. Ueber die industrielle und national-ākonomische Bedeutsamkeit der Gewinnung von Chemikalien insbesondere des Paraffin's und Photogen's aus dem Kohlentheer, w. S. w. Aschersleben, Beyer, 1856. This article must here close. Leaving unnoticed several inaccuracies which we had intended to discuss we will dismiss the subject with two brief quotations. The first from Dr. Antisell's book, p. 15. “An impression has taken hold of the American manufacturing public that the patent of James Young has no force, as it was not a new invention at the date of the patent; and from the unfavorable effect of that patent upon the actual manufacture of coal-oils in this country, an ill-feeling has been produced against it. That the owners of this patent have not acted wisely by witholding sales and licenses under it until very lately, is to be regretted; but that it was a bona fide improvement in an art at the time when it was patented, and that therefore the patent was rightly issued in this country, there can be no shadow of a doubt in the mind of any one who carefully traces the steps of the discovery of the production of photogenic oils from different materials.” The second from Lord Chief Justice Campbell's charge” to the jury in the case already alluded to. “Now gentlemen I direct you, in point of law, that if there were books then [at date of Young's patent, 1850] in circulation in England disclosing this mode of obtaining paraffine and paraffine oil which were known, were accessible, that the patent would be invalid, although Mr. Young never read those books, and although that mode had not been actually put in practice. If there were books in England in circulation, accessible to all who were interested in the subject, which disclosed this, and would instruct them and enable them to obtain the paraffine and the paraffine oil from the distillation of bituminous substances, then Mr. Young's patent would be invalid.” FRANK H. StoreR.

s C I E N T I FI C IN T E L L I G E N C E .

1. On a probable means of rendering visible the Circulation in the Eye; by OGDEN N. RooD, Prof. of Chemistry in Troy University.—Some time ago while looking at a bright sky through three plates of cobalt-glass, I saw with astonishment that the field of view was filled with, and traversed in all directions by small bodies resembling animalcules.

They were seen on the blue field as yellowish spots, and always appeared elongated in the direction of their motion, which was as a general thing tolerably uniform. The same result was obtained by experimenting upon the eyes of a number of persons.

Convex lenses of various foci, (from 3 in. to 4 in.), were now held before the eyes, so as to give the blue light various degrees of convergence and divergence, without in the least altering the appearance of the moving bodies; this seemed to indicate that their locality was in the retina or in its immediate neighborhood.

A position near the axis of vision was selected, and observed, when it was found that these bodies in traversing this spot always pursued the same direction and path, disappearing at the same point; other positions near the axis gave like results.

* Loc. cit., p. 520.

This would seem to preclude the possibility of the moving bodies being animalcules swimming in the humor of the eye; the most probable remaining supposition is, that they are blood-corpuscles circulating in the retina or in its immediate neighborhood. The apparent diameter of these bodies when seen projected on a window six feet distant may be about go of an inch, which corresponds to about room of an inch on the retina. The average diameter of the blood globules is garo of an inch, but taking into account the fact that the shadows of the moving bodies are not well defined the correspondence may be considered pretty satisfactory.

The question now arises as to the manner in which the blue glass renders the circulation visible, for these moving shadows cannot be seen with distinctness through red, orange, yellow, green, nor even purple media ; they are on the other hand well shown by a certain thickness of a solution of the cupro-sulphate of ammonia.” Yellow solutions when combined with the blue glass or blue solutions render the circulation invisible, and it does not reappear till the yellow solution has been made so dilute as barely to preserve a yellow tint, and to transmit the spectrum almost unaltered. This shows that the indigo and violet rays are principally concerned in the production of this appearance, but that it cannot be attributed to fluorescent properties in the blood discs is indicated by the fact that the circulation can be seen through a considerable thickness of crown glass, through an infusion of red sanders wood mixed with ammonia, as well as through a solution of the disulphate of quinine.

The only explanation that has occurred to me as being probable is the following: the blood discs are yellow and consequently opaque to a great extent to the indigo and violet rays; they would therefore in passing before the retina cast shadows on it; now the retina being already strongly impressed with blue light, that portion of it which was momentarily protected from the action of this light, would experience the complimentary sensation—or would see instead of a moving shadow a yellowish moving streak. This explains also why the appearance is not seen with any distinctness in red, orange, yellow, or green light, for yellow media are to a great extent transparent to all their rays and therefore fail to cast shadows. These observations: if new may be of some interest to those engaged in the study of the physiology of the eye.

Troy, May 14th, 1860.


1. Care of Platinum Crucibles.—In connection with some sensible remarks upon the use of sand in cleaning platinum crucibles, a practice which, with Berzelius, (Lehrbuch der Chemie, 1841, 4th Aufl. p. 516,) he heartily commends—urging that it should be employed every time that a crucible is used, ERDMANN explains the cause of the gray coating which forms upon platinum crucibles whenever they are ignited in the flame of Bunsen's gas-burner.

This coating has given rise to much annoyance and solicitude among chemists. Indeed it has often been asserted, that the use of Bunsen's

# Mr. Wm. B. Taylor of Washington to whom some of these facts were communicated by Prof. J. Henry was able to trace this appearance, though with diminishing distinctness, through plates of bluish-green and yellow glass. AM. JOUR SCI.-SECOND SERIES, Vol. XXX, No. 89.-SEPT., 1860.

burner is unadvisable in quantitative analysis, since by means of it the weight of platinum crucibles is altered and the crucibles themselves injured. The coating is produced most rapidly when the crucible is placed in the inner cone of the flame, and the more readily in proportion as the pressure under which the gas is burned, is higher. Having found it advantageous to maintain, by means of a special small gas holder, a pressure of four or five inches upon the gas used in his own laboratory, Erdmann has observed that the strong gas flame thus afforded, immediately occasions the formation of a dull ring upon the polished metal placed in the inner flame, this ring being especially conspicuous when the crucible becomes red hot; it increases continually so that after long continued ignition the whole of the bottom of the crucible will be found to be gray, and with its lustre dimmed. This ring is caused neither by sulphur, as some have believed, nor by a coating of inorganic matter, but is simply a superficial loosening of the texture of the platinum in consequence of the strong heat; whence it first of all appears in the hottest part of the flame. In conjunction with Pettenkofer, Erdmann instituted several experiments which have left but little doubt that the phenomenon depends upon a molecular alteration of the surface of the metal. If a weighed polished crucible be ignited for a long time over Bunsen's lamp, the position of the crucible being changed from time to time in order that the greatest possible portion of its surface shall be covered with the gray coating, and its weight be then determined anew, it will be found that this has not increased. The coating cannot be removed either by melting with bisulphate of potash or with carbonate of soda. It disappears, however, when the metal is polished with sand; the loss of weight which the crucible undergoes, being exceedingly insignificant, a crucible weighing 25 grams, having lost hardly half a milligram. When the gray coating of the crucible is examined under the microscope it may be clearly seen that the metal has acquired a rough, almost warty, surface, which disappears, when it is polished with sand. Platinum wires which are frequently ignited in the gas flame, for example the triangles which are used to support crucibles, become as is known, gray and brittle. Under the microscope they exhibit a multitude of fine longitudinal cracks which as the original superficial alteration penetrates deeper become more open, or as it were spongy—until finally the wire breaks. If such wire is strongly and perseveringly rubbed with sand, the cracks disappear, and the wire becomes smooth and polished, for the grains of sand acting like burnishers restore the original tenacity of the metal; very little of its substance being rubbed off meanwhile. The loosening effect of a strong heat upon metals is beautifully exhibited when silver is ignited in the gas flame; a thick polished sheet of silver immediately becoming dull white when thus heated. Under the microscope, the metal appears swollen and warty. Where it has been exposed to the action of the inner flame along its circumference, this warty condition is visible to the naked eye. A stroke with the burnishing stone however, presses down the loosened particles, and reproduces the original polish. This peculiar condition which the surface of silver assumes when it is ignited, is well-known to silversmiths, it cannot be replaced by any etching with

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