The Optical Magic Lantern Journal (April 1899)

53 twelve hundred must be brought upto the same density as its neighbour, and the whole strip | must present no stains or abrasions of the film. Various are the methods by which this apparently superhuman task is brought within | the capabilities of mortal man. At first sight it would seem that some form of winding mechanism—possibly similar to that in the taking © apparatus itself—would reduce the matter to the range of practicability, but o little con| sideration will reveal the weak points of such a | course. It will be sufficient to recall the fact , that celluloid film coated with gelatine is not of a nature to be wound over itself upon a spool » when the said gelatine is wet. The horror of | tackling such a length of delicate and light' gentitive material, loose and uncontrolled, in a tub full of liquid, needs not the penning of a weird description to bring it home to the mind of the most daring man. Yet it is possible that — for short trial pieces of film, at all events a series of large tubs, containing a plentitude of © developer, alum, fixing salts, etc., the film being drawn hand over hand from one to another, might not after all present insuperable difficulties | to the careful operator. But it ig usual and probably very much wiser | to employ one of the devices that experience |, has shown to be applicable to the case, and by whose help the dark-room manipulations are shorn of most of their terrors. One method, which is largely practised in America, is that in which the film is wound upon a huge drum before development, and retained thereon during that and all subsequent operations. The drum | is pivoted at the centre and the film wound | around it so that the various turns lie side by » side, and not over one another as ona spool. | Supposing that the periphery of the drum is wide enough to accommodate 10 turns of the film side by side—which is 15 inches without allowing for the small spaces which in practice are unavoidable—it would require rather over 8 feet in circumference, or, say, 1 yard in | diameter, and allow a little for emergencies, to | accommodate a film of average length. Another plan which finds more favour in England is that in which a cross-frame of peculiar construction is employed, and it has the advantage that it occupies much less space and is therefore more convenient to handle, and a | _ idea of the nature of this device. smaller quantity of developer is necessary while every portion of the film is beneath the surface of the solution during the whole operation of development. This last is a valuable consideration, for it at once opens the door to many developers that would be debarred by the other ' method on account of their easily oxidisable nature. The accompanying sketch will give an It will be seen that the cross is of the shape accredited to St. Andrew, and each of the arms is studded with a large number of perpendicular pegs of ' the same height as the width of the film to be wound upon them. The method of winding is just the reverse of that where the drum method is employed. Whereas in that case the . film was wound in the form of a cylindrical _ spiral, in this it is in the form of a flat spiral like a watch spring. Practically the winding is the same as if it were upon its original spool, but each layer is separated from the next by four of the pegs. When the film is entirely wound upon the cross the whole thing is simply ‘treated like a large photographic plate and submerged in the developer until the examina‘tion by transmitted proclaims that the operation has been carried sutticiently far. light of any portion (To be continued.) —— TRS NEW APPARATUS. & 93% ‘©COMPENSATOR’’ ACETYLENE GAS GENERATOR. Mr. W. C. Hughes, of Kingsland, has taken up the agency for an acetylene generator of foreign invention termed the ‘“‘ Compensator,"’ and has given us the opportunity of trying it ' over an extended period. This we have done, and now give a description of the apparatus itself and also its mode of behaviour. The gas is generated by means of water reaching the calcium carbide from below, so that as goon as water has reached the carbide the generated gas immediately drives the water back again until more gas is required. The gas is then led through a spiral pipe surrounded by water for cooling purposes towards the burners. When using gas formed in this manner, it is requisite to have some means of storing any