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Welding glass in optical contact
March, I917.]
CURRENT TOPICS.
369
hole about a quarter of an inch in diameter, we can see the subject through it from any part of the plate area. In this way we practically turn the camera into a finder of the frame type, and this is all tl~at is necessary, actual focussing being neither required nor possible. Ferro-cerium and Other Pyrophoric Alloys.
C . R . ]~OHM.
(Metal Record and Electropl~ter, vol. iii, No. I, p. 8, January, 1917. ) --About the year i9o 3, Welsbach discovered that certain alloys of the rare earths, when filed, gave off showers of bright sparks which would readily ignite inflammable gases. It was subsequently found that the best results were secured when employing an alloy carrying about 65 per cent. cerium earth metals and about 35 per cent. iron. The same action takes place with these alloys as wi.th the flint and steel, except that a spark is more easily produced than with the primitive tinder-box. The mixture of cerium earth metals, often called misch metal, consists mainly of the elements cerium, lanthanum, didymium, neodymium, praseodymium and samarium. All of these metals are white or light yellow in color and are not readily oxidized in air. When first produced, the price of ferro-cerium alloys was $60 per kilogram. Later, this was reduced to $12 per kilogram, and in 1913 to about $4.60 per kilogram: The present return to the old price is, of course, due to the abnormal conditions which have affected nearly all products. While the original pyrophoric alloy or ferro-cerium manufactured by Wels.bach contains nearly 40 per cent. of iron, the competing products possess only about 15 per cent. of iron, and for the purpose of hardening, about 2 per cent. of antimony or bismuth is added. Silicon is, of course, found in nearly all ferro-cerium alloys because it is either contained in the raw misch metal as an impurity, or has been absorbed from the clay crucibles in which the alloy is often produced. T o insure a low-melting and smooth-casting pyrophoric alloy, certain manufacturers add about 5 per cent of copper. Most manufacturers produce ferro-eerium by the electrolysis of the anhydrous chlorides of cerium, lanthanum, didymium, etc., and it is necessary that cheap current be available. Many manufacturers use ordinary graphite or clay crucibles with large iron cathodes; others use water-jacketed iron crucibles. Welding Glass in Optical Contact.
G . R . PARKER AND A. J.
DALLADAY. (Enc~ncering, vol. ciii, No. 2663, p. 23, January 12, 19t7.)--For many optical researches glass cells are wanted, formed by two strictly parallel walls or windows, and different pieces of giass, lenses and prisms, etc., have frequently to be united in such a way as to keep the surfaces optically true. Glass surfaces can be polished without difficulty to be so nearly plane or so nearly of the same curvature that they show less than one interference fringe per inch when placed together and examined by light reflected from the
37 °
CURRENT TOPICS.
[J. F. I.
interfaces. These surfaces may be brought into optical contact so that the two pieces of glass act optically as if they were one block by applying a pressure of several pounds per square inch. Unions so made may be easily separated by sudden heating or cooling by a shearing force, or by the application of liquids which gradually creep in between the surfaces. A cell constructed of plates of glass in optical contact with a separating piece of U-shape could be made very accurately parallel; but the surfaces could be too easily separated again. Various cements like Canada balsam are, of course, largely used in optical combinations. But it is difficult by their aid to insure parallelism within one minute of the arc, and if the walls of the cell form a wedge of an angle of only a few seconds, instead of a cavity with plane-parallel walls, interference work may be seriously impaired. If pieces of glass could be welded without affecting the optical truth of their surfaces, considerable advantages would be gained. Attempts to effect such optical junctions by heating have been unsuccessful so far, though bifocal lenses are made by uniting two lenses either by cementing or ,by fusing ; in the latter case, however, the flint is readily fused, and optically true contact is not aimed at. The authors have su.cceeded by experiments in the research laboratories of Messrs. Adam Hilger, Limited, in producing some excellent specimens of optical welding. The secret of success lies, as might be expected, in the selection of the proper temperatures and pressures. It was found essential that the temperature at which union took place should not only be far below the melting point of the glasses to be joined, bu.t also below the annealing temperature, for even at that latter temperature very slight strain would cause deformation of worked glass surfaces. At 6o degrees C., below the annealing temperature, it was found that two pieces of glass in optical contact would unite within an hour, and any slight deformation produced by the compression could be renledied by a few strokes of the polishing tool. Lithographic Stone in the United States. ANOn;. (U. S. Geological S1*rvey Press Bulletin, No. 3o8, February, I917.)--In 1916 for the first time there was a considerable production of lithographic stone in this country. This production, according to information received by G. F. Loughlin, of the United States Geological Survey, Department of the Interior, was made by the Kentucky Lithograph Stone Company, which has quarries at Brandenburg, Ky., and an ofrice in Louisville. In 1916 the company sold 4o,ooo pout~ds of finished stone at prices ranging from 2 ~ to 27 cents a pound. For some years previous small quantities had been sold occasionally in Louisville, but in I916 the stone was shipped to buyers as far away as Cleveland, Washington, New York and Boston. The quarry at Brandenburg contains three distinct beds from which lithographic stone may be obtained. Two of these beds are
CURRENT TOPICS.
369
hole about a quarter of an inch in diameter, we can see the subject through it from any part of the plate area. In this way we practically turn the camera into a finder of the frame type, and this is all tl~at is necessary, actual focussing being neither required nor possible. Ferro-cerium and Other Pyrophoric Alloys.
C . R . ]~OHM.
(Metal Record and Electropl~ter, vol. iii, No. I, p. 8, January, 1917. ) --About the year i9o 3, Welsbach discovered that certain alloys of the rare earths, when filed, gave off showers of bright sparks which would readily ignite inflammable gases. It was subsequently found that the best results were secured when employing an alloy carrying about 65 per cent. cerium earth metals and about 35 per cent. iron. The same action takes place with these alloys as wi.th the flint and steel, except that a spark is more easily produced than with the primitive tinder-box. The mixture of cerium earth metals, often called misch metal, consists mainly of the elements cerium, lanthanum, didymium, neodymium, praseodymium and samarium. All of these metals are white or light yellow in color and are not readily oxidized in air. When first produced, the price of ferro-cerium alloys was $60 per kilogram. Later, this was reduced to $12 per kilogram, and in 1913 to about $4.60 per kilogram: The present return to the old price is, of course, due to the abnormal conditions which have affected nearly all products. While the original pyrophoric alloy or ferro-cerium manufactured by Wels.bach contains nearly 40 per cent. of iron, the competing products possess only about 15 per cent. of iron, and for the purpose of hardening, about 2 per cent. of antimony or bismuth is added. Silicon is, of course, found in nearly all ferro-cerium alloys because it is either contained in the raw misch metal as an impurity, or has been absorbed from the clay crucibles in which the alloy is often produced. T o insure a low-melting and smooth-casting pyrophoric alloy, certain manufacturers add about 5 per cent of copper. Most manufacturers produce ferro-eerium by the electrolysis of the anhydrous chlorides of cerium, lanthanum, didymium, etc., and it is necessary that cheap current be available. Many manufacturers use ordinary graphite or clay crucibles with large iron cathodes; others use water-jacketed iron crucibles. Welding Glass in Optical Contact.
G . R . PARKER AND A. J.
DALLADAY. (Enc~ncering, vol. ciii, No. 2663, p. 23, January 12, 19t7.)--For many optical researches glass cells are wanted, formed by two strictly parallel walls or windows, and different pieces of giass, lenses and prisms, etc., have frequently to be united in such a way as to keep the surfaces optically true. Glass surfaces can be polished without difficulty to be so nearly plane or so nearly of the same curvature that they show less than one interference fringe per inch when placed together and examined by light reflected from the
37 °
CURRENT TOPICS.
[J. F. I.
interfaces. These surfaces may be brought into optical contact so that the two pieces of glass act optically as if they were one block by applying a pressure of several pounds per square inch. Unions so made may be easily separated by sudden heating or cooling by a shearing force, or by the application of liquids which gradually creep in between the surfaces. A cell constructed of plates of glass in optical contact with a separating piece of U-shape could be made very accurately parallel; but the surfaces could be too easily separated again. Various cements like Canada balsam are, of course, largely used in optical combinations. But it is difficult by their aid to insure parallelism within one minute of the arc, and if the walls of the cell form a wedge of an angle of only a few seconds, instead of a cavity with plane-parallel walls, interference work may be seriously impaired. If pieces of glass could be welded without affecting the optical truth of their surfaces, considerable advantages would be gained. Attempts to effect such optical junctions by heating have been unsuccessful so far, though bifocal lenses are made by uniting two lenses either by cementing or ,by fusing ; in the latter case, however, the flint is readily fused, and optically true contact is not aimed at. The authors have su.cceeded by experiments in the research laboratories of Messrs. Adam Hilger, Limited, in producing some excellent specimens of optical welding. The secret of success lies, as might be expected, in the selection of the proper temperatures and pressures. It was found essential that the temperature at which union took place should not only be far below the melting point of the glasses to be joined, bu.t also below the annealing temperature, for even at that latter temperature very slight strain would cause deformation of worked glass surfaces. At 6o degrees C., below the annealing temperature, it was found that two pieces of glass in optical contact would unite within an hour, and any slight deformation produced by the compression could be renledied by a few strokes of the polishing tool. Lithographic Stone in the United States. ANOn;. (U. S. Geological S1*rvey Press Bulletin, No. 3o8, February, I917.)--In 1916 for the first time there was a considerable production of lithographic stone in this country. This production, according to information received by G. F. Loughlin, of the United States Geological Survey, Department of the Interior, was made by the Kentucky Lithograph Stone Company, which has quarries at Brandenburg, Ky., and an ofrice in Louisville. In 1916 the company sold 4o,ooo pout~ds of finished stone at prices ranging from 2 ~ to 27 cents a pound. For some years previous small quantities had been sold occasionally in Louisville, but in I916 the stone was shipped to buyers as far away as Cleveland, Washington, New York and Boston. The quarry at Brandenburg contains three distinct beds from which lithographic stone may be obtained. Two of these beds are