The Optical Magic Lantern Journal (May 1895)

86 The Optical Magic Lantern Journal and Photographic Enlarger. their ends, and bubbles of gas will soon be seen to come off from the copper plate. As a means of forming a ready method of connecting the two wires together, the following simple key will be found useful in this and other experiments, or any of the numerous forms that are in use and can be bought for a few pence at every electrical dealers. The method of constructing the key is as follows :—Two pieces of brass are secured, each by two screws, to a suitable base of mahogany, the pieces of brass overlapping one another, but one bent so that when in its normal state not to be touching one another, as shown in the lower portion of Fig. I. ; the wires for connecting are secured to the two outer screws, which must be of brass also. When it is required to make contact it is only necessary to press the finger upon the part marked (x), and the circuit will be completed and will remain so as long as the pressure of the finger is kept there. The arrangement shown in Fig. II. will clearly illustrate the electrolysis of slightly acidulated water. ’ Pure water being a bad conductor of electricity, it is it a better one by adding a_ slight quantity of acid. In this experiment a tank of the same description as that shown in this Journal, page 189, November, 1894, is used. Two pieces preferably of platinum wire are bent round at one end to form an eye, and the other ends are inserted through the india-rubber separating the sides of the tank. Place the tank in the lantern as in the former case, and connect the loops or eyes (MN) to the wires froma battery, A small bichromate battery about a pint capacity will be . found the handiest for experiments of this ; description, as by raising or lowering the zinc element the strength of current is more under’; control, besides giving off no destructive fumes to destroy any brass work that may be brought in close proximity to it. The small key described above and used in the preceding experiment will be found useful in this experiment also by inserting it in the circuit. As soon as contact is made gas will be seen to be given off from the platinum points surrounded by the acidulated water. By placing two inverted test tubes filled with the acidulated water over the platinum rods gas may be collected. The gases will be seen to come off more rapidly from the one than the other, and will soon make itself apparent by the difference of the volume necessary to make ; é ) L ; the quality of the water used in their prepara of gas in the two tubes and consequent lowering of water. The gas evolved from the negative pole will be twice as great as that which collects at the positive pole. Another experiment, showing the effect of the current, can be shown by stitching together several thicknesses of blotting paper and placing it in the tank, dividing the tank into two portions; pour in on both sides of the porous diaphragm so formed a solution of sulphate of soda coloured with litmus. Colour the solution on one side of the porous diaphragm in which the negative electrod is red, by adding to it one or two drops of dilute acid. When the circuit is completed it will be seen that the blue becomes red, and the red blue, and by reversing the poles an opposite effect will be obtained. —— <0: its Effect on Our Work. Water and By Duncan Moore. THE purity and brilliance of our transparencies and negatives are considerably influenced by tion. Chemically, pure water exists mainly in theory, rather than for any available supply. Distilled water being the nearest approach to it we are likely to get, and that very often is far from what it professes to be. The mystic capitals HO, represent the chemical constitution of water, but the component parts of the water we have to avail ourselves of would be more nearly represented by all the letters in the alphabet. Pure water consists of a mixture by weight of eight parts of pure oxygen gas with one part of pure hydrogen; if it contain anything else it must exist as an impurity. The sea is the primary source of all water, by evaporation, it is carried over the land by clouds, and is discharged from them as rain, to afterwards present itself as river, spring, and wellwater. Rain-water if collected at a long distance from towns, or manufactories, or other sources of contamination, and at a great altitude is the purest form of natural water, but even under these conditions it is not absolutely pure, as a certain amount of foreign matter floating in the atmosphere is carried down with it, That, however, collected near towns is on the contrary extremely impure, the air being greatly contaminated with anmoniacal and other detrimental vapours that impregnate it, to say nothing of the thousand-and-one impurities in the dust lodging on the roofs, etc., from which the