The Optical Magic Lantern Journal (April 1895)

66 The Optical Magic Lantern Journal and Photographic Enlarger. a liquid assumes when the disturbing effects of weight are thus got rid of, is by suspending one liquid in another, both of which are about the same specific gravity. Olive oil is lighter than | water but is heavier than alcohol, but with neither does it mix, so that by mixing the alcohol and water we can obtain a liquid of the same specific gravity or nearly so to that of olive oil, or a similar oil. In a glass tank in the lantern place the mixture of alcohol and water, equal quantities of each will be found about the right proportion, into the centre of mixture by means of a long pipette, as in Fig., a quantity of olive oil, and if the mixture is in the right proportions a sphere of oil should be formed which will be found to suspend itself, as it were, in the place where the oil is introduced ; but if not so, then the oil will rise and sink according to which of the component parts is in excess. Should it rise, then add more alcohol and stir. If, on the other hand, it sinks, add more water. Another series of interesting and beautiful phenomena caused by cohesion is what are termed ‘‘ Tomlinson’s cohesion figures,’’ many of which can be well shown by means of the vertical attachment. Professor Tomlinson has spent much time in the study of these figures, and for papers written by him. To the individual, apart from the projecting with the lantern to a large audience, there is work for many an instructive winter's evening. When a drop of any of the essential oils are placed upon water a figure is produced which in some cases is very pleasing in form, and it is believed that every independent liquid, as Professor Tomlinson calls it, produces a different figure when placed upon water. The following are a number of the ‘substances mentioned by him: cod-liver oil, sperm oil, colza oil, turpentine, creosote, oil of lavender (pure), oil of corrander, oil of cinnamon, alcohol, and acetic ether. By mixing two of istics of both oils, and in this way he was Introduce | enabled to detect the adulteration of many of the oils sold, especially those for which a high price is paid, such as cod-liver oil, which is adulterated with common fish oil, and oil -of lavender, which is adulterated with turpentine. For performing the experiments to be observed individually, simple round saucers will do, but for exhibiting by means of the vertical attachment a flat bottomed glass dish, as described in | this Journal, page 217, vol. 5, answers the pur pose well. As the oils are only to bo used in drops, small quantities of each are only required. Get | as many small bottles as you can and go round the cupboards and shelves on a foraging expedition for oils. Before going to work the following are some of the causes of frequent failure: 1, want of purity in vessels and water used ; 2, care in delivering the drop; 3, care in keeping _ the surface of the water tranquil. Having arranged your vertical attachment with the clean water in it on the horizontal condenser, dip a needle or a piece of rod glass : drawn to a point into the oil so as to get a drop ' of the oil upon it, allow the first one or two drops to fall until a steady one is formed upon the needle or glass rod, then bring it gently down to the centre of the surface of the liquid and let it fall, then focus upon the screen. It is as well to have the surface of the water already in focus by dropping a piece of paper on the water and focussing it. Whilst in some cases the phenomena lasts some few minutes upon the surface of the water, at other times it is only momentary and takes place in the fraction of a second as when acetic ether is used, whereas a drop of cod-liver oil produces a figure that lasts much longer. All the oils mentioned are not capable of being readily thrown upon tie screen, but no doubt many i , : readers will try the experiment without the full information concerning their causes the | reader must consult some of the numerous | lantern. The following books could be consulted for more information upon the subject, ‘Tomlinson’s Encyclopedia of Useful Arts and Sciences,”’ (Volume ITI., appendix), also Philosophical Magazine, 1861. 70: | Oxygen—When Doctors Differ, Who is to Decide? THERE seems to have been some little competition of late as to the relative qualities of the ; OXygen gas made by two firms, and both have the oils a figure is formed having the character° t . tion tested by experts. had their own make and also that of the opposi