written on this subject it may appear strange that anything could be added at this late date. But if we stop to examine some of the methods proposed and used we will see that they are far from ideal. Pyro has been used in photography since 1851, but no one thought of a preservative until 1882 because it was not until dry plates came into use that an alkaline pyro solution was necessary. The pyro solution used previous to this date was acid or more rarely neutral. A preservative is something which will prevent the pyro from oxidizing before having accomplished its purpose.

Exception may be taken to the statement that salts of sulphurous acid act as or are preservers of pyro, for it is well known that sodium sulphite will oxidize with greater or lesser rapidity according to conditions. It was recently found that certain organic compounds even if only traces of them are present, will greatly retard the absorption of oxygen by sodium sulphite in solution. So that, when we have a solution containing sodium sulphite and pyro they will mutually preserve each other. However, it is also well known that sodium sulphite is alkaline and under such conditions pyro will rapidly absorb oxygen, but to prevent this various schemes have been proposed, to neutralize this alkalinity with various acids, or to add some acid to the pyro solution and mixing the sulphite with the alkali.

As the Lumière brothers recently pointed out, the presence of salts in the developer which do not take part in the development only retards the action. At present there are at least four compounds containing sulphurous acid suitable for the preservation of pyro (and of course other alkaline developers); they are: Sodium or potassium metabisulphite, acetone-sulphite and sodium bisulphite.

In this paper I shall consider only sodium bisulphite as a dry salt to distinguish it from the liquid bisulphite. The reason for choosing this compound is because it does the work equally as well and is much cheaper. As sodium sulphite has a retarding effect, experiments were made to see if there would be any advantage in using a pyro developer without sulphite on plates having a short exposure such as snap-shots.

The strength of the developer was pyro one grain, anhydrous sodium carbonate eight grains and water one ounce.

It was found that a small quantity of sodium bisulphite did not influence the development, but did prevent the developer from oxidizing rapidly. The images on the plates had the same qualities whether the developer contained sodium sulphite or not. Tests were then made to determine the smallest practical quantity of sodium bisulphite necessary to preserve the pyro and the subsequent developer.

To obtain the best results one grain of pyro requires two grains of sodium bisulphite (a larger amount is unnecessary.) This amount of pyro and sodium bisulphite requires eight grains of anhydrous sodium carbonate. The above amounts in one ounce of water yield the best results for all ordinary work. The maximum amount of pyro per ounce of developer was found to be four grains.

For convenience two stock solutions are made, one containing pyro, eight grains, sodium bisulphite, sixteen grains; and the other, anhydrous sodium carbonate sixty-four grains, to every ounce of water. Thus every dram of pyro solution contains one grain of pyro and the alkali eight grains of anhydrous sodium carbonate; in other words equal volumes should be used. One to two drops (not more) of a ten per cent. potassium bromide solution to every ounce of the developer will keep the plates clear if they have a tendency to fog. This small amount of bromide does not influence the development. I have a pyro solution made ten months ago, the stock bottle only partly filled, yet it has only a faintly yellow tint. Sodium bisulphite is a dry white powder, the solution has an acid reaction. In price it is the same as any good quality of sodium sulphite.

FILM PACK DEVELOPMENT.

S

By GEORGE RETTIG.

OME of the ANNUAL readers may be interested in a method of using the developing tank for "Film packs."

The accompanying illustration shows a rack for holding the cut films during development, fixing and washing. Two strips of wood have grooves about one-eighth of an inch deep sawed in them. After being made waterproof they are fastened together, the top and bottom of

Pin

Pin

Pin

Pin

the rack being left open. The films are slid into the grooves and held in place by pins pushed through holes drilled across the grooves and as near the face of the strips as possible. These pins also keep the films from touching each other during development. After being thoroughly wetted to prevent air bubbles, they are developed and fixed in the usual manner.

A piece of stiff wire sharpened to a chisel point makes a good awl to drill the pin holes with.

THE PHOTOGRAPHIC MAGAZINE

AND ITS READER.

By FAYETTE J. CLUTE, Editor "Camera Craft."

HE average reader of a photographic magazine feels that he could give the editor some valuable pointers on the getting out of a publication that would more nearly fill the requirements, and he sometimes goes to the trouble of putting his advice into written or spoken words. His suggestions are always acceptable and if they are not acted upon it is because they are for good reasons unpractical. On the other hand, the editor feels that he could give a few words of advice that would enable the reader to derive more benefit from his favorite magazine. I have always been a very indefatigable reader of the literature of photography and as I still retain a very vivid recollection of my first efforts to acquire a working knowledge of photography from the, at that time, limited available literature of the craft, a few suggestions may not be out of place.

To begin with, do not neglect the articles that seem at the time to be too far advanced for your comprehension. Much of the information which such an article contains will be of no direct value at the moment but all unconsciously you will be absorbing valuable information that will piece in with other like material and as you come up to the subject later you will find that you have a good working knowledge of the plan or process. Even if the article covers a process which you never have occasion to use, the information gained concerning it will be of value, one photographic process dovetailing into another so closely. Describing an early experience of my own will perhaps convey a better idea of my meaning. A very technical article on lens construction was carefully studied through, despite the fact that it was mostly Greek to me at the time. A little later another article was encountered that attempted to explain the location of the nodes of emission and their importance in calculations to determine the conjugate focus. This in turn was but little more clear than