When this is thoroughly accomplished, mix a portion of your tripoli with the dilute nitric acid, to the consistence of thick cream. Then take a pellet of cotton and well polish the plate with this mixture, in the same manner as with the rottenstone. Continue the process till, on removing the tripoli with a clean pellet, the plate exhibits a clear, smooth, bright surface, free from all spots, or scratches. Any remains of the acid on the plate may be entirely removed By sifting on it a little Drying powder, and then wiping it carefully off with a fine camels hair brush, or duster. The finishing polish is now to be given. For this purpose the rouge--or a mixture of rouge and lamp-black, in the proportion of one part of the former to seven of the latter--is used. It should be kept either in a muslin bag, or wide mouth bottle, over which a piece of muslin is tied--in fact, both the rottenstone and tripoli should be preserved from the dust in the same manner. With a little of this powder spread over the buff--described on page 53--the plate recieves its final polish; the circular motion is changed for a straight one across the plate, which, if intended for a portrait, should be buffed the narrow way; but if, for a landscape or view of a house, the length way of the plate. The operation of cleaning the plate at first appears difficult and tedious, and many have been deterred from attempting this interesting art on that account; but, in reality, it is more simple in practice than in description, and with a little patience and observation, all difficulties are easily overcome. Great care must be taken to keep the buff free from all extraneous matter, and perfectly dry, and when not in use it should be wrapped up in tissue paper, or placed in a tight box. The plate should be buffed immediately before the sensitive coating is given; particles of dust are thus effectually removed; the temperature of the plate is also increased by the friction, and the required tint more readily obtained. SECOND OPERATION.--Applying the sensative coating.--The apparatus and chemicals required, are an Iodine box--see fig. 14 page 53. Bromine box--similar to the iodine box but a trifle deeper. Dry Iodine. Bromine, or a compound of Bromine and Chloride of Iodine, or other sensitive mixture. Most of our best operators use the compound Bromine and Chloride of Iodine. In the early days of the Daguerreotype, Iodine alone was used in preparing the plate, and although it still plays a very important part, other preparations, called accelerating liquids, quickstuff, &c., are used, and the discovery of which has alone ensured the application of the Daguerreotype successfully to portrait taking--for when first introduced among us it took from five to ten minutes to produce a tolerable good view, while now but the fraction of a minute is required to obtain an accurate likeness.