The strength of the positive bath must be regulated by the strength of the negative. The stronger the negative, the weaker the bath may be. For a moderately strong negative, the bath may be between sixty and sixty-five grains to the ounce. Very thin and weak negatives require a bath of seventy to eighty grains. - Elbert Anderson. 18

248. As the solution becomes reduced in strength, always add pure crystals of silver, and not a stronger solution of ammonia, as some recommend, as in that case the ammonia soon becomes in excess, and is liable to dissolve off the albumen. The proper plan to adopt is, as the solution is reduced in strength, to add pure nitrate of silver, and, when it is reduced in bulk, to make a fresh supply according to the formula, and mix them together; this will keep your solution at a certain standard all the time. The paper should be floated on this solution from one to three minutes, according to the density of the negatives in use. Take just as much care of this solution, too, as you would of your negative-bath solution. When not in use, keep it covered up from the air and dust, or

Now paper requiring a bath of one hundred grains should contain, for each unit of surface, two and a half times as much of the soluble chloride as that requiring a forty-grain bath. It follows, then, that each sheet silvered on a one hundred-grain bath should convert two and a half times as much silver as the forty-grain bath, while the free nitrate of silver withdrawn from the bath by the paper will contain the same proportionate excess. It will not be much out of the way to say that an ounce of silver made into a forty-grain bath will silver two and a half times as many sheets as the same quantity of silver in a one hundred-grain solution. This is on the supposition that the strength of the salting varies in the same proportion as the silver. The one hundred-grain bath will give more free nitrate to be washed from the prints, and more unreduced chloride to be removed by the fixing-bath.

It is a matter of no small importance, on the score of economy, whether a strong or weak solution is used, provided, as is claimed, the weaker solution is not used at the expense of some quality of excellence in the resulting picture. But, as above intimated, much depends upon the preparation of the paper, for the salting may be such that a forty-grain bath would dissolve part of the albumen, sufficient to impair the brilliancy of the print. Suppose a paper salted with a chloride whose base gives a very deliquescent nitrate which has not the property of coagulating albumen. It is probable that, on floating this paper on a forty-grain bath, so much silver would be converted into the chloride from the solution in immediate contact with the surface of the albumen, that the impoverished solution, aided, it may be, by the new nitrate, would dissolve a portion of the albumen. In such case the silver bath must be strengthened, and I remember to have used paper that for the best results required a bath one hundred and twenty grains strong. - W. H. Sherman.

248. When a new bath is made, add about half an ounce of ammonia to the gallon. The precipitate of oxide of silver is left on the film, and will dissolve when the bath is filtered again after it has been used for ten or twelve sheets. If at any time discoloration should appear again, look to the strength of your solution, and use a few drops of ammonia. The ammonia added to the printing-bath produces, to a more or less degree, the effect of fuming, according to the quantity which is used. How or why the addition of ammonia prevents discoloration, I am unable to tell. Per contra, if the bath be very strong, the solution will repel from the surface, which will look greasy, the liquid collecting in drops. - Charles Waldack.

Take nitrate of silver, fuse it, dissolve it in the necessary quantity of water, put it in the sun for a few days, and filter it. When tested, now, with litmus-paper it will turn red paper else nightly pour it in to a bottle where no containing influences can reach it. It will treat you well if you are good to it, and reward you with splendid results.

249. A few words as to the manner of sensitizing or floating the paper. First, turn up the corners of the sheet, albumenized side down, so it may be readily handled by them. Now seize the sheet by the two diagonal corners, and allow it to fall or curve, the right end being lifted the blue. Now add C. P. nitric acid, enough to turn a piece of blue litmus - paper red, My within ten or fifteen second. Let it stand for a day or two, and throw into it precipitated chalk (ten cents' worth will go a long ways; an excess will do no harm). After a day or two, during which time it must be well shaken up once in a while, filter it carefully, and you will find that this silver solution will not turn blue paper red, and yet work rapid and without fig. I forgot to state that it has to be saturated with iodide of silver, as usual, chalk is also good to use in discoloring silver solution for silvering paper. I always keep some in my funnel, through which I let the solution run after being used. - R. Benecke.

Let me say that you may, on the utilization of old negative baths for printing, take any old negative bath, no matter if it fogs or has been overworked. If acid, neutralize either with carbonate of soda or liquor ammonia, a slight excess of alkali does not matter, and set in the sun for an hour or so; if there is no sun, keep it in the light as long as you can. The object of this is to precipitate all organic and other impurities, while retaining the alcohol in the solution. When sufficiently sunned, add one drachm of a solution of citric acid (sixteen grains to the ounce of water) to every eight ounces of bath solution. The object of this is to precipitate the iodide of silver in the bath. Filter, and add fresh silver until the solution contains thirty-five grains to the ounce. Now. to every half gallon add half an ounce of muriatic acid; shake well, then add enough liquor ammonia to make it slightly alkaline; again shake well, filter, and save the filtering-paper for subsequent use as long as you can. Every time you strengthen, add a little acid and ammonia. Float the paper from thirty to forty seconds; no more. Fume as usual. - J. L. Gihon.