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if the regularity be destroyed by rapidly moving the plate in irregular directions while breathing upon it, irregular patches of color are produced which are the analogues of natural colored clouds. In fact the rich colors of the sunset are but broken and irregular interference halos.

Wood smoke seen in large quantities as from piles of burning brushwood, is strongly blue. As we pass nearly into a line with the sun, having the smoke between us and it, the color becomes less decided, until when the light becomes almost direct, it is yellow. A red or yellow diffuse light produced by interference caused by spherical globules, will always be weaker than the corresponding blue light, for the same reason that the transmitted spectra of thin plates are weaker than those reflected, viz: the great difference in the intensities of the interfering beams. Consequently, until we pass nearly into a line with the sun it is chiefly the blue interference light that reaches

the eye.

Philadelphia, March, 1869.

Art. XXXVI.Process for determining the Carbon chemi

cally combined with Iron ; by Prof. EGGERTZ, Director of School of Mines, Falun, Sweden.*

When steel or pig iron containing carbon in chemical combination is dissolved in nitric acid, a soluble brown coloring matter is formed whose coloring power is quite intense, and the solution assumes a tint which is dark in proportion to the quantity of the chemically combined carbon.

Iron and graphite (or free carbon) do not influence this coloring ; for the solution of nitrate of iron is colorless, or at most slightly greenish, unless extremely concentrated, and graphite is insoluble in nitric acid.

Thus in dissolving two pieces of different steels of the same weight in nitric acid, taking care to dilute the darker solution until the two liquids present exactly the same color, it is very evident that the more highly carburetted steel will furnish the larger quantity of liquid, and that the proportion of the volumes will indicate the relative proportion of color in the two steels.

If now the composition and content of carbon of one of the steels is known, the absolute per centage of carbon in the other steel may be immediately deduced.

* From the Bulletin of the Chemical Society of Paris; translated for this Journal by J. Wharton, Esq.

Suppose that 1 gram of each of two steels (a and b) have been dissolved, and that the volumes of the two solutions brought to the same degree of coloring bear the relation to each other a : 6:: 5:7. Knowing that the steel (a) contains 1 per cent of carbon, you at once deduce that the steel (6) contains 1.4 per cent of carbon.

In applying this method of analysis, certain precautions must be taken, which we proceed briefly to point out.

In a cylindrical test tūbe dissolve gradually in the cold 10 centigrams of wrought iron, steel, or cast iron reduced to a fine powder, in 14 to 5 cubic centimeters of nitric acid of 1.2 specific gravity (about 25° Baumé). The use of nitric acid containing hydrochloric acid must be avoided because the solution of iron would have a yellow tint.

In proportion as the metal contains more carbon, more nitric acid must be used. After some time, when the chief part of the metal appears to be attacked, place the tube in a waterbath to the depth of about fifteen millimeters, and warm it to 80° centigrade. In this position only the lower part of the tube is in contact with the warm water; a movement takes place in the acid which favors its reaction upon the metal ; a slight disengagement of carbonic acid from all the particles of carbon may be observed. The operation should always be conducted under the same circumstances as to heat and length of time.

The evolution of gas having ceased in operating upon steel the reaction must continue two to three hours), place the tube in a large vase filled with water to bring the solution always to the same temperature. This precaution is indispensable because the same liquid is darker when warm than when cold. Afterward, pour off as exactly as possible the clear liquid into a graduated burette. Upon the black residue remaining in the tube pour some drops of nitric acid and heat carefully over a lamp. If there is no further liberation of gas, the residue consists of nothing but graphite or silica. Cool the new solution and add it to that which is already in the burette.

The liquid is then diluted with water until its color corresponds exactly with that of the normal liquid, which latter should be of such a degree of concentration that each cubic centimeter represents .0001 gram of carbon.

If, for instance, this normal liquid is prepared from cast steel containing exactly 1 of one per cent of carbon, one decigram of that steel must be dissolved in 8.5 cubic centimeters of nitric acid ; 100 grams of steel containing 85 centigrams of carbon would thus be dissolved in 8500 cubic centimeters of the normal solution, 100 cubic centimeters of that solution would represent one centigram of carbon, and consequently one cubic centimeter of the normal solution would represent .0001 gram of carbon.

The normal solution does not keep, and should be often renewed, since it becomes perceptibly paler even within 24 hours. For it however may be substituted a dilute alcoholic solution of sugar properly caramelised brought to exactly the same tint ; this solution keeps much longer without sensible change.

As one gram of iron cannot readily be dissolved in less than 15 cubic centimeters of nitric acid, it follows that a proportion of carbon less than 10 of one per cent, * cannot be estimated by means of the normal liquid, but this minimum is seldom found in practice.

If the proportion of carbon exceeds of one per cent, the ferruginous solution is so concentrated that it has a light greenish tint, which renders its comparison with the normal liquid difficult. In that case a normal liquid of one-third the strength is prepared by diluting the normal liquid with twice its volume of water; then each cubic centimeter of the liquid represents only one-third of the ten thousandth part of a gram of carbon. When the proportion of carbon in the specimen to be analyzed is very large (as for instance in white cast iron) only .05 gram of the metal must be taken for analysis, and in that case half a cubic centimeter of its solution corresponds to a cubic centimeter of the normal solution. If the metal to be analyzed contains graphite, the latter must be collected on a filter before the solution is put into the burette.

This method is more exact in proportion as the percentage of carbon is smaller. With an accurate balance, and with suitable arrangements, a great number of determinations of carbon close enough for practice can be effected in a time relatively

very short.

All the Bessemer steel made at Edskin in Sweden is marked after hammering (apres l' étirage) by figures expressing its hardness as ascertained by this color-measuring analysis of Prof. Eggertz.

It is obvious that only burettes of perfectly colorless glass must be used, or at least they must all have exactly the same tint.

* 0. D. Allen of the Freedom Iron Works, Penn., has found it quite practicable by a modification of this method to distinguish between irons containing respectively 1o and it's of one per cent of carbon.

ART. XXXVII.-Geographical Notices; by D. C. GILMAN.

ARCTIC RESEARCHES. 1. Dr. I. I. HAYES continues to commend to public attention the importance of sending out a new American expedition for the survey of the Polar basin, entering by Smith's Sound. The following summary of his project is printed in the New York Tribune.

First: as to design. The design of the expedition which I have proposed is to complete the exploration of the entire region northward of Baffin's bay: to trace Greenland and Grinnell Land to their termination ; then ascertain if other lands lie to the northward ; to explore the Open Polar Sea ; and lastly to reach the North Pole, making upon the course such observations as circumstances will allow. Thus will a field be opened for the most valuable discoveries, in geography, geology, in glacier formations, magnetism, countries and currents, and in natural history. Second: as to plan. I would set out in May with two vessels, one a small steamer, and would make my course northward, provided with the best chart of Greenland, through the Middle ice, until I reached Smith's Sound, in latitude 78° 17', where, in my old harbor of 1860–61, I would pass the winter.

the winter. Here there is abundance of game, and I would found a colony. Walrus, seals, reindeer, and foxes, could be caught in great numbers, and not only would the colony be made self-sustaining, in point of food, but a valuable cargo of furs and oil might be collected. Then I would push northward the next summer with the steamer, and would thus strike for the North Pole. In any case, I would secure a harbor, and a base of operations much to the north of the colony, and thus would the steamer and the colony become the centers from which the explorations already mentioned would be made. Third : As to cost. A public-spirited citizen of New York has offered to supply a suitable steamer, and there is good reason to suppose that we could obtain from the government the loan of a sailing vessel, one of the many not in use. These vessels furnished, they could be equipped and maintained in the field through two summers and two winters, at a cost of $40,000. Fourth : Let it be remembered that this is the American route.” The land extends there further north than in any other quarter so far as known, and Americans have thence explored to within less than eight degrees ; that is to say, within 450 miles of the Pole. Independent, therefore, of the value to science of this particular line of discovery above AM. JOUR. SCI.-SECOND SERIES, VOL. XLVII, No. 141.-MAY, 1869.

any other in the unexplored parts of the Arctic regions, there is something of national honor involved in the pursuit of it, especially at this time when England, France, Germany, and Sweden are each aiming to reach the North Pole by various other routes ; to which end expeditions are now actually preparing. Shall we let those nations win from us the coveted honor of priority? I do not believe there is a single person within the sound of my voice who would be indifferent to the matter, and who would not unite to see the American flag first planted at the North Pole. Fifth As to the advantages of the Smith's Sound route over all the other routes, for discovery in the unexplored parts of the Arctic regions, they are but the simple enumerations which I have before made to the Society : 1. Land as a base of operations ; 2. The opportunity to colonize a party of hunters and natives as the means to a permanent support.”

2. Capt. Silas BENT, late of the U. S. Navy, who rendered important hydrographical services in the Perry expedition to Japan, and who was also attached to the Preble under Capt. Glynn in an earlier visit to Japan, has also published his views on the subject of the best mode of reaching the North Pole. They are found in a lecture given before the Missouri Historical Society in St. Louis, Dec. 10, 1868, which embodied two brief communications to the American Geographical Society of New York. (This is printed in a pamphlet of 30 pp. with a map, St. Louis, R. P. Studley.) Capt. Bent while on the coast of Eastern Asia made important observations on the Kuro-Sirvo or Japanese Gulf Stream, which presents some very interesting analogies to the American Gulf Stream.* These observations are contained in the second volume of the Report of the Perry expedition. In his opinion, every attempt to reach the North pole should be made by following the continuation of one or the other of these gulf streams, that is, through Behring's straits or by the Spitzbergen route, which he terms the " thermometric gateways to the pole.” He is therefore decidedly opposed to the project of Dr. Hayes for an expedition through Snith’s Sound. His views, though formed independently and upon his own observations and studies, coincide in many respects with those which are held by the continental geographers in Europe.

3. The very interesting observations on the coast of “ Wrangell's Land,” in the Arctic ocean, made in 1867 by Captain Long of an American whaling vessel, and announced in the Pacific Commercial Advertiser, have awakened a great deal of comment in the European journals; and have led Dr. Petermann

* Originally suggested by W. C. Redfield, this Journal, xxv, 131, (1834), xlv, 301, (1843).

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