A Manual Of Photography

TO GIVE THE SENSITIVE SUBFACE TO THE PLATE. 247 accelerator ; or by combining the chloro-iodide of lime with a little of the bromide, a mixture similar to that of M. Guerins may be produced: but I greatly prefer, and would recommend, the pure bromide of lime, it being, as I believe, the quickest accelerating substance at present known. By slightly colouring the plate with the chloro-iodide, and then exposing it for a proper time over the bromide, proofs may be obtained in a fraction of a second, even late in the afternoon. A yellow colour should be given by the use of the first substance ; and the proper time over the bromide is readily obtained by one or two trials.1 With about a drachm of the substance 111 a shallow pan, I give the plate ten seconds the whole of the first day of using the preparation, and add about three seconds for every succeeding one. The compound should be evenly strewed over the bottom of the pan, and will last, with care, about a fortnight.. “ The great advantage of this compound is, that it may be used continuously for a fortnight without renewal ; and, unlike bromine water, its action is unaffected by the ordinary changes of temperature.”, The advantages of employing a dry material are so great that the bromide of lime is now commonly employed. By the employment of these agents a sensitive coating is produced, upon which actinic changes are almost instantly made. The modes of proceeding to prepare the plates are similar to those already named.. The time necessary for the plate to be exposed to the action of the bromine water, if it be used, must be determined by experiment, for it will vary according to the size of the box and the quantity of liquid used. It is ordinarily between thirty and sixty seconds, the time varying with the temperature of the atmosphere: when once determined, it will be constant with the same box, the same strength of solution, and the same temperature. , , The method of coating the plate which is most approved is as follows:—Place the pan upon a table, fill the pipette with bromine water, draw out a little way the glass slide, and allow the bromine water to run into the pan, and again close the vessel: the liquid must cover evenly the bottom of the pan; 1 better to count time both over the iodine and the bromide of osure of the plate to the iodine, after it has received its pro- nolhon of SoSne should be one-third of the time it took to give it the first coating of iodine. We have found that if less iodine than this be allowed to the plate it will not take up so much mercury, neither will the picture produced be so bold and distinct.