The Optical Magic Lantern Journal (January 1899)

surface with the metal. It may here be noted that in most—if not all-_of these methods powdered aluminium may be employed instead of magnesium, and that the following remarks will apply equally to both metals. The most usual form of flash light is that in which the powder (pure metallic magnesium) is blown through a gas or spirit flame. Here, on the face of it, we might say, is absolute safety ; pure magnesium is not explosive, and hence may be used with impunity. This is, however, a dangerous fallacy; flour is nonexplosive, yet many a mill has been wrecked by the explosion of a mixture of flour and air, and magnesium under similar circumstances becomes an explosive of no mean power. The real danger in lamps of this type lies in | the liability to “suck back” the flame when | the pressure on the ball is released, while there is a quantity of the lighter particles of the metal in a state of temporary suspension in the reservoir. All the conditions for a miniature bomb explosion are here present, and the result has been in some cases more disastrous than if the affairs had been planned with malice aforethought. To the writer’s knowledge the interior of a room has been wrecked and the windows blown out through the explosion of an , innocent-looking lamp little larger than an egg, the operator fortunately severely burned hand; and as a minor accident we can instance the bursting of a rubber ball in the hand, the flame from the lamp having traversed nearly 2 feet of rubber tubing drawn into the ball during previous exposures. The moral of this is that the simplest lamp is the safest. That a simple bent tube carrying the requisite quantity of powder, which is at once blown into the flame and consumed, is the most effective and the least risky. those with a large reservoir for the powder, there should be an efficient back pressure valve, which should prevent the ball from refilling with air through the same channel by which it has escaped. Several lamps have been introduced in which the magnesium powder has been mechanically projected into the flame, but in these there has always been a tendency to throw the powder in a body, and thus to cause imperfect combustion. It is, however, in the use of explosive mixtures composed of magnesium or aluminium mingled with chlorate of potash, or its equivalent, that the greatest danger lies. Some of escaping with a : If more elaborate | lamps of the magazine type are used, especially | 4 The Optical Magic Lantern Journal and Photographic Enlarger. these require to be mixed immediately before use, as it kept they are liable to spontaneous combustion, while others will keep without deterioration or danger for a considerable time. As a general rule the danger in using them is the same as when employing gunpowder or dynamite, viz., the general liability to accidental explosion. This varies according to the composition of the powder; with some the slightest spark is sufficient to cause ignition, while with others a heated wire or a detonator of some sort is required, It is perhaps hardly necessary to point out the advisability of packing up the requisite quantity for each exposure in a separate package and of, as far as possible, isolating these packages from each other, thus preventing the recurrence of such an accident as caused serious injury if not death to the operators some years ago in America. In tkis case a professional photographer and his assistants were engaged in photographing at the top of a high building, using an explosive flash light mixture, which was kept in an open box and ladled out as required ; a stray spark reached this stock, and, as might naturally have been expected, a violent explosion ensued, coping stones and other portions of the building being detached and hurled down into the street below. It may seem unnecessary to repeat the caution against using any explosive powder in a lamp with a more or less closed reservoir, but a recent accident which has cost the | experimenter dearly proves that this danger before firing the loose powder which had been ' is not yet appreciated by many at its true value. Nothing but pure metallic magnesium must be put into an ordinary flash lamp. Explosive powders must be fired upon a metallic plate or dish, and this should be firmly fastened to its support or the shock of discharging may throw it down carrying with it a portion of red hot ash or other residue and thus igniting curtains or furniture. Flash sheets, consisting of a film of collodion carrying in its substance the necessary quantity of magnesuim, or sheets of paper impregnated with chlorate of potash and covered with magnesium, would seem to present some advan . tages; at least, they cannot witbout considerable trouble be put into alamp. The only danger attaching to their use is common to all flash lights, viz., the production of a large and intensely hot flame which may reach and ignite drapery, scenery, or other inflammable articles if carelessly produced in their close proximity. In conclusion, the writer wishes to disclaim