Water 40 ounces. Nitrate of silver 1800 grains. Measure the water, and put into a two-quart bottle; then pour out 8 oz. of it in a pint bottle, and into this put the whole of the nitrate of silver (1800 gr.); shake it well until it is all dissolved. This forms a concentrated solution--into which put the following prepared iodide of silver:-- Dissolve in a 3 or 4 oz. bottle containing 1 oz. water, 10 gr. nitrate of silver; and in another bottle or graduate containing a little water, dissolve 10 grains of iodide of potassium; pour this into the 10 grain solution of nitrate of silver, and a yellow substance (iodide of silver) will precipitate; fill the bottle with water, and let it settle; then pour off the water, leaving the yellow mass behind; again pour on it clean water, shake it, and let it settle as before, and pour off again; repeat this for about six changes of water. Then it (the iodide of silver) is to be put into the bottle containing the 8 oz. water and 1800 gr. of nitrate of silver; shake it well, and it will nearly or quite all dissolve; pour this into the two-quart bottle, and shake well; it will be of a yellowish white tint, and should be filtered through asbestos or sponge, when it will become clear. When clear, test the solution with blue litmus-paper; if it turns it red, it is sufficiently acid; if it does not change it, add _one_ or _two_ drops of nitric acid, chemically pure; then test it again; if it does not change it, add _one_ or _two_ drops more, or just enough to change the paper to the slightest red. A solution prepared in this proportion will, like others, improve by age. An old bath is considered far more valuable than one newly prepared. These remarks may appear to old photographic operators as of no importance, but they must bear in mind that there are hundreds just adopting this new process of picture taking. This solution will work more satisfactorily than the one I formerly used. It will work quicker in the camera, and is _equally_ durable. * * * * * Acknowledgment.--The following pages, under the head of _Vocabulary of Photographic Chemicals_, and treating upon the Chemicals used in Photography, are taken from the third edition of "Hardwich's Photographic Chemistry:"-- =Vocabulary of Photographic Chemicals.= [Sidenote: VOCABULARY OF PHOTOGRAPHIC CHEMICALS.] Acetic Acid. Symbol, C{4}H{3}O{3} + HO. Atomic weight, 60. Acetic acid is a product of the _oxidation_ of alcohol. Spirituous liquids, when perfectly pure, are not affected by exposure to air; but if a portion of yeast, or nitrogenous organic matter of any kind, be added, it soon acts as a _ferment_, and causes the spirit to unite with oxygen derived from the atmosphere, and to become _sour_ from formation of acetic acid or "vinegar."