QUICK DRYING OF NEGATIVES.

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By ERNEST A. TURNER.

HEN we speak of drying a plate or film negative, we refer to the removal of the water absorbed by the gelatine coating or coatings (in the case of non-curling film.) For simplicity, let us consider first only a dry plate negative. We shall then have simply a sheet of glass coated on one side with the gelatine emulsion "film coating." The sheet of glass deserves no particular consideration. It serves simply to support the "film coating." The glass is entirely impermeable to the solutions and washwaters, it does not absorb and does not become "wet" in the true sense. Of course some drops of water will adhere to a glass plate when it is immersed in water, but this water does not penetrate even to a ten-thousandth part of an inch. This is easily proven by wiping and rubbing the plate with a clean soft linen cloth. The water on the surface of the glass is entirely absorbed by the linen and the surface of the glass becomes dry immediately without any time being necessary for evaporation to take place. The gelatine film coating is quite different. It absorbs water greedily. The film coating on an ordinary dry plate is one-thousandth of an inch thick, but place the plate in water for half an hour or carry the plate through the usual processes of developing, fixing and washing and the film coating swells up to tenthousandths of an inch. The gelatine has absorbed nine times its own volume of water and it is this water that must be again taken from the gelatine before the plate negative is dry.

Ordinarily we simply expose the plate to the air until the water in the gelatine has entirely evaporated. Now for the ways to hasten the drying.

The first is to remove the water from the film coating by immersing the negative in some liquid which has a stronger attraction for water than the gelatine has. Such a liquid is ordinary alcohol. Immerse a wet negative in alcohol for a few minutes and most of the water is taken up by the alcohol.

The film coating shrinks in thickness and when the negative is removed from the solution what liquid it contains is not simply water but a mixture of alcohol and water which evaporates much more readily than water. The drying is hastened first by there being less liquid to evaporate and second by that liquid being more vaporizable. The negative dries in a few minutes. It is not necessary to use ordinary or "grain" alcohol for this purpose. Denatured alcohol answers equally well and is much cheaper. A pint wide-mouth bottle of denatured alcohol will hasten the drying of a large number of negatives before it becomes too much diluted. It is used over and over and the wide-mouth bottle is suggested simply for the reason that it avoids the need of using a funnel when pouring the alcohol back from the tray to the bottle.

A second method of quick-drying involves the use of formaldehyde. Formaldehyde has a very strong tendency to "harden" gelatine and to make it insoluble. It is this same tendency that in alum produces that "puckery" feeling when a crystal of alum is applied to the tongue. The alum takes the water out of the tongue,-shrivels it. Alum does the same thing to gelatine, so does formaldehyde, only with formaldehyde the effect is many times stronger. When the wet negative is immersed for a few minutes in a five per cent. solution of formaldehyde the gelatine film coating gives up most of its water and shrinks or shrivels in thickness. At the same time, it becomes insoluble and capable of resisting heat. The negatives may now be removed and quickly dried in a moderate heat without fear of the film coating softening and running.

The same effect is produced in a less degree by alum. Chrome alum is a much more powerful hardener than ordinary alum. A negative which is fixed in the usual Chrome Alum Fixing and Hardening bath does not carry nearly as much water in the film coating, and may be dried by a moderate heat. This hardening, of course, overcomes all hot weather troubles since it enables the gelatine to stand the higher temperature of fixing bath and wash water without softening. The softening tendency of the developer is not so important since the negative only remains in the developer for a very few minutes.

The film conditions are exactly similar to those of the glass

plate. The film is simply coated on celluloid instead of glass and the celluloid, to all intents and purposes, resists wetting with water the same as a glass plate. Non-curling film, however, is coated on the back with Chrome Alum hardened gelatine so that there are two surfaces to dry instead of one. This does not affect the rapidity of drying, however, as each surface has its own exposure to the atmosphere.

A CEMENT SINK.

By A. B. STEBBINS.

HE advantage of a cement sink for photographic use are absolute security against leakage, cleanliness, and cheapness. If you follow the directions you can make one that will be a luxury compared with the ordinary wooden sink, and at a trifling cost in labor and cash. The most important point is a good foundation, that is, a solid box so supported that there will be no settling or spring. Make your box four inches wider and two inches deeper than you want the inside dimensions of the sink, use good one inch lumber, (it can be cheap but should be sound; rough hemlock is all right,) have it well nailed together, put it in the place used and have the drain pipe well fitted at this stage.

I recommend that the cement bottom be two inches thick, so run the pipe through the box one and three-quarters of an inch so as to let the cement set around it, which it will hold tighter than if it were screwed in. See that it is fixed in the right place and stop it with a cork. It will be a good plan to put a union just below the sink if you are at all likely to want to disconnect it at any time.

The cross section, Fig. 1, shows the box ready to be filled. You will see that all the pattern or mould needed is a wooden frame four inches less in width, two inches less in height, (outside measurement) than your box. It is supported even with the top of the box by narrow strips tacked on so as to hold it in place equidistant from the sides and two inches from the bottom; these strips are indicated in Fig. 2.

Now get your mason and have him put in the cement. Tell him to handle it dryer than he would for cement walks as it will drip through some, (no need of any tight joints in the box.) Let it set from two to three hours when you can pull the mould away and it is ready for troweling. Now let it set over night and it will be ready for use in the morning.

Get the best Portland cement, and good clean sand. One half barrel of cement and three bushels of sand will make a sink 3 x7 feet inside. I use three parts of sand, two parts cement. If you have any confidence in your mason let him decide these points. I have put two such sinks in my workrooms; got things ready, had the mason fill the moulds between five and six p. m.; they were ready to trowel between nine and ten p. m. and were in use next morning.

To finish the sink put a facing of planed lumber around the top indicated in Fig. 2 and let it project one-fourth of an inch inside (this is to protect the edges.) I also use a planed piece of wood in the front of the box. A coat of paint gives it the finishing touch. If you think it necessary you can reinforce the sides, corners and bottom of the sink by putting big nails or spikes in the cement. Have these completely buried and they will not rust. Heavy wires can be run in through the bottom, but if you have a solid box, good cement and clean sand, these are not essential.

None of the chemicals used in ordinary work will effect such a sink except strong acids. It does not absorb and retain moisture or odors; developers do not stain it and it can