244. Of all methods of developing films the developing machine or tank is the simplest, and with this simplicity is included the possibility of the very finest results.

245. By the tank method, of course, the action of the developer upon the film is all concealed - you see nothing until the negatives are completely developed, and, therefore, were you to begin your instruction with tank development you would not have a real knowledge of negative developing. For this reason it is essential that anyone intending to become thoroughly proficient in negative making first learn to develop in an open tray, where they can watch the operation and see what they are doing, and observe the progress of development of the latent image. In this way alone will you learn to understand and know what is to be expected from films exposed under various conditions. With a knowledge of the process of development based upon this practical experience, simplified methods may be employed and the developing tank brought into practical use.

246. From the foregoing it must not be inferred that the developing tank cannot be used from the very beginning. It can be employed successfully before the student has any experience with tray development whatever, but it is not possible for that student to have the practical knowledge of negative making that is so essential if his individuality is to count for anything in his work.

247. For the amateur who cares nothing about the whys and wherefores - whose only desire is to secure records of vacation scenes, home surroundings, etc., for the pleasure of having such records, doing away with all bother - then the tank may be employed from the start. On the other hand, however, if negative making is to be thoroughly understood, then tray development, where one can watch the image grow, must be employed. Only with a knowledge of what is to be accomplished thoroughly impressed upon the mind can one appreciate the advantage of tank development and employ it intelligently.

248. The best known type of machine or tank for film development is the Eastman Film Tank. (See Illustration No. 27.) This tank is the successor to the original film machine, which was the first practical instrument of its nature, and in which the exposed film was enfolded in a protective celluloid apron, and at the same time made to rotate in the developing solution for a fixed period of time. The tank method differs from the machine, in that the exposed film is rolled up with the protective celluloid apron in one operation, and then the two together are brought into a tank or receptacle containing the developing solution, and there left for a given period of time, according to the strength and the temperature of the developer. This method is simpler than the former, in so far as the film does not require to be continuously rotated enabling the operator to proceed with some other work.

249. All tank development is based on the factors of time and temperature. A given strength of developer at a cer~

Illustration No. 27.Eastman Film Tank.

Illustration No. 27.Eastman Film Tank.

See Paragraph No. 248.

Illustration No. 28.Winding Box.

Illustration No. 28.Winding Box.

See Paragraph No. 254.

Illustration No. 29.Premo Cut Film Developing Tank.

Illustration No. 29.Premo Cut-Film Developing Tank.

See Paragraph No. 259.

Eastman Film Tank.

tain temperature, requires a given time for development. This is the principle back of all tank or stand development.

250. The normal temperature for developing solutions is between 60° and 70° Fahr., although in summer, or in tropical countries, the temperature should not be over 60°. When the developer is warm it works rapidly and produces a coarse grain on the film. When cold it acts slowly; therefore, to obtain uniform results it is necessary to have some knowledge of the effect of temperature and the speed of the developer before attempting to develop.

251. When prepared developing powders are used carefully follow the manufacturer's directions for preparing the solution. It is very important to have the developer mixed in exactly proper proportions each time.

252. A separate hypo dish should be provided for fixing the films. In the absence of a regular fixing box it is advisable to employ a shallow dish of good size, or a small pail. Use a liberal supply of solution which will cover the films well.