The Optical Magic Lantern Journal (November 1893)

168 The Optical Magic Lantern Journal and Photographic Enlarger. scissors; the flask is then gently placed on the mouth of a gallipot as a support. The difficult task of getting the crystals out of the liquid, without damaging them, is next described; a glass rod, with a little circular glass plate attached to it by wax upon a part of the edge of the plate, is pushed down the neck of the inclined flask, the glass circle is pushed gently beneath the largest crystal, then raised from the liquid by a depression of the hand, and drawn out. All fluid is then taken up thoroughly from the glass disc by blotting paper, and this must be done without touching the crystalline surface ; the crystal is then dried by exposure to the air in a room having a temperature of 40° or 50°F. It is sometimes necessary to dip the crystals for an instantin a little cold distilled water containing a little iodine, After being again dried they are placed under a cupping glass, having a watch glass containing a few drops of tincture of iodine, which materially improves the power of polarisation of the crystal. About three hours of this exposure to the iodine vapour may be necessary, in a room having the temperature of 50°F. He then describes how to mount the crystals by covering them with another piece of thin microscope glass, and cementing them with very thin Canada balsam, without the application of much heat, What has been said will give a fair idea of the process, but Mr. Herapath’s full description of the operations is too long to quote here. In the Philosophical Magazine for May, 1854, and for May, 1855, are other articles by Mr. Herapath on the same subject. When the temperature of the room does not fall below 50° or 55° F., he advises the use of the following proportions :— Disulphate of quinine ... 100 grains. Acetic acid, sp. gr. 1:042. 4 fluid ounces. Rectified spirit, sp. gr. 0°837 ... ... 1 fluid ounce, Spirituous solution of iodine... ‘ 1 fluid drachm, The crystals are produced more rapidly with this formula, and must be removed in three or four hours, or the mother liquid will dissolve them. We have but given a brief outline of the methods of Mr. Herapath, but have stated enough, perhaps, to enable any experimenter who wishes to make himself an adept at the production of such polarisation crystals, to make a beginning, but for full information he should refer to the original memoirs. Inside some Saturators. SEEING that many people still look upon saturators with a certain amount of suspicion, we thought it might tend to allay their unfounded fears if we gave them an opportunity of seeing the internal arrangements of certain saturators, and thus enabling them to have sufficient confidence in this method of producing the limelight to try one themselves. After so doing we have no hesitation in saying that those who have hitherto set their faces against saturators will welcome this method as a reliable one of producing a brilliant illumination of the mixed jet principle with the aid of one bottle of gas only, and that oxygen. Our readers may remember that in the April number of this journal we gave a diagram of the single form of the Lawson saturator. Quite lately this saturator has been devised to serve a double lantern. The saturator for this purpose is, from the outside, not unlike two of the single saturators described at the time spoken of. The portion for the lower lantern does not differ from the particulars we gave, excepting that the lime is now made to turn from the back instead of the side. The portion of the saturator for the upper lantern is as shown. The oxygen is ades mitted at a. The stream is \ then divided mM) by the tap, @| that which is =B| Conducted to a) thelowerpori} tion of ‘the saturator passes upwards through the stuffing 8, which has previously had a charge of ether placed in it, mai The oxygen ii thus saturajted passes = > out at D, and the mixing chamber zr, at thence reaches which time it becomes equivalent to the hydrogen of ordinary mixed jet. According to the : regulation of the tap a stream of pure oxygen is allowed to pass vid the tube c to the jet, r | vepresents the lime for the upper lantern.