Put into the bromine box a given quantity of this solution, sufficient to well cover the bottom; the plate, having been iodized to a deep yellow, is placed over it; the time the plate should be exposed must be ascertained by making a few trials; it averages from twelve to forty seconds. When once ascertained, it is the same for any number of plates, as the solution, which of course would become weaker and weaker, is changed after every operation, the same quantity being always put into the pot. Chloride of Iodine.--This is prepared by introducing chlorine gass into a glass vessel containing iodine; the iodine is liquified, and the above named compound is the result. Operators need not, however, be at the trouble and expense of preparing it, as it can be obtained perfectly pure of Mr. Anthony, 205 Broadway, N. Y., as also all of the chemicals herein enumerated. The compound is diluted with distilled water, and the plate submitted to its action till it is of a rose color. Chloride of iodine alone, is seldom if ever used now by American operators, as it does not sufficiently come up to their locomotive principle of progression. The next is also eschewed by the majority, although many of our best artists use no other, on account of the very fine tone it gives to pictures. Bromide of Iodine.--This is a compound of bromine and chloride of iodine. In mixing it, much depends upon the strength of the ingredients; an equal portion of each being generally used. Perhaps the best method of preparing it, is to make a solution in alcohol of half an ounce of chloride of iodine, and add the bromine drop by drop, until the mixture becomes of a dark red color; then dilute with distilled water, till it assumes a bright yellow. Put about half an ounce of this compound into the pot, and coat over it to a violet color, change the solution when it becomes too weak to produce the desired effect. Another.--Mix half an ounce of bromine with one ounce of chloride of iodine, add two quarts pure distilled water, shake it well and let it stand for twelve hours then add twenty-five drops of muriatic acid, and let it stand another twelve hours, occasionally shaking it up well. Dilute six parts of this solution in sixteen of water. Coat over dry iodine to a deep yellow, then over the sensitive to a deep rose color--approaching purple--then back, over dry iodine from four to eight seconds. Roach's Tripple Compound.--This is one of the very best sensitive solutions, and is very popular among Daguerreotypists. To use this, take one part in weight, say one drachm, of the compound and dilute it with twelve of water; coat over dry iodine to yellow, then over the compound to a rosy red. The effect in the camera is quick, and produces a picture of a fine white tone.