Grant that there is an analogy between the above-mentioned cases, then the cause and effect become intelligible. First we have a hard-sized paper with gases or air condensed in the interstices, and with the external air adhering to it; in this condition it is coated with an amorphous film of albumen. All appears to go on favourably until the fixing process; here the temperature is reduced by the addition of water contained in the prints. Now the absorbed air which the water contains finding a nucleus on its permeating the body of the paper grows immediately (as I pointed out when directing your attention to the phenomena proceeding from the freezing of the water) in the surface-fibre, thus it is likely that the blisters are formed is all cases where air is enclosed. Hyposulphite of soda when entering into solution reduces the temperature considerably—the air being then held with so little force readily unites with a nucleus.
To counteract this natural effect it is obvious that means should be taken to prevent the lowering of the temperature on the addition of water to the hypo, solution, or on the transference of prints from the hypo, into water containing absorbed air.
If this be unmanageable, the easiest thing to do is to dip the prints into methylated alcohol, after leaving the toning bath. This treatment removes the sizing from the paper, and the prints appear translucent while wet. They should now be _well washed_; any disengaged air will then be able to escape through the porous body of the paper. It has been recommended to employ a large charcoal filter to absorb the air or gases, but, like all filters, it will require cleaning out, and the charcoal needs re-burning.
A word on filters in conclusion. The public purchase filters, and imagine that they are to have pure water, or clarified solution, for evermore without trouble; let them be undeceived, because when charcoal becomes saturated it must be re-burned to restore its purifying properties.
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IN last week’s issue your idea of combining silver with a new base in the collodio-bromide is so good that I think it just as well to mention that the very notion of acetate of silver has been carried out by me a dozen years ago, although in another form. I made a collodion for wet-plate work in which an iodide was used with about an equal part of acetate of soda; the collodion was accelerated to such a degree that my exposure was reduced to about a fourth of what I would have given without the acetate. The plate developed beautifully and free from fog. Here, again, comes in the law of compensation; my thoroughbred collodion was, at the end of a dozen hours, as slow as a team of oxen, as vitality seemed to expend itself in one _coup d’état_, and the second day it was capital——for cleaning plates.