Mix, and when dissolved, take one part to three of collodion, as before. I feel certain that on a strict adherence to the correct proportion depends all the success of photography; and as we find in the kindred process of the daguerrotype, that if we add too much or too little of the bromine sensitizer, we make the plate less sensitive, so in this process. When making the first of these sensitizers, I always in each case let the solution attain a temperature of about 60º before decanting, so as to attain a perfectly equable compound on all occasions. In the second, or ammonium sensitizer, the solution may be assisted by a moderate heat, and when again cooled, may advantageously be filtered to separate any sediment which may exist; but neither of these liquids should ever be exposed to great cold. I dissolve in my bath of nitrate of silver as much freshly precipitated bromide of silver as it will take up. Next, as to the printing of positives to obtain black tints, the only condition necessary to produce this result is having an acid nitrate bath; whether the positive be printed on albumen paper, or common salted paper, the result will always be the same. I have tried various acids in the bath, viz. nitric, sulphuric, tartaric, and acetic, and prefer the latter, as being the most manageable, and having a high equivalent. The paper I now constantly use is common salted paper, prepared as follows. Take Chloride of barium 180 grs. Chloride of ammon. 100 grs. Chloride of potassium 140 grs. Water 10 oz. Mix, and pour into a dish and lay the paper on the liquid, wetting only one side; when it has lain there for about five minutes if French paper has been used, if English paper till it ceases to curl and falls flat on the liquid, let it be hung up by a bent pin to dry. These salts are better than those generally recommended, as they do not form such deliquescent salts when decomposed as the chloride of sodium does, and for this reason I should have even avoided the chloride of ammonium, only that it so much assists the tints; however, in company with the other salts, the nitrate of ammon. formed does not much take up the atmospheric moisture, and I have never found it stain an even unvarnished negative. To sensitize this paper take Nitrate of silver 500 grs. Acetic acid, glacial 2 drs. Water 5 oz.