Complaint is sometimes heard regarding the difficulty of getting negatives of sufficient strength. It may be well to consider the variouscauses for weak negatives. During the short days of late fall, winter and early spring, the light, even at noon time, does not have as much strength and does not possess the actinic quality of daylight during the summer when the sun is higher. The difference in photographic value of light at the various seasons of the year is not always given due consideration. For this reason there is always a tendency to undertime during the short days.

There are also various other causes for thin negatives. Incorrect temperature and lack of strength in chemicals will produce insufficient density. If the subject is properly lighted and exposure correct, the cause for weak negatives must be attributable either to incorrect temperature or chemicals not working with sufficient energy.

One of the great advantages derived from Tank development is the ease of maintaining proper temperature during the entire time of development. With tray development in a cold room, the temperature of the solution, even if at the proper point when development begins, will often drop low enough before development is completed to prevent yielding negatives having the desired pluck and brilliancy.

The temperature of the dark room has a very important bearing on results, but when unable to keep temperature of the dark room at the proper point, it will assist materially in maintaining a correct temperature of the developer to fill the tray with hot water just before placing plates and developer in same. Another good plan for maintaining an even temperature of developer was given in "Practical Suggestions" of the January number of the Studio Light.

By maintaining the temperature at the correct point of 65 to 70 degrees, the cause for trouble may often be traced to the chemicals. Having eliminated the questions of proper lighting, exposure and temperature of developer, as possible causes for insufficient density, we arrive at a consideration of the chemicals used. If a formula has the proper proportions of Pyro, Sulphite and Carbonate, either by weight or hydrometer test, and gives weak, flat negatives, no attempt should be made to secure more density by increasing the amount of Pyro. The probability is that the developer is lacking in Carbonate. The office of this agent is to act as an accelerator which, by opening the pores of the gelatine, permits the reducing agent (Pyro) to act more energetically on the granules of silver which have been affected by exposure to the light. The presence of Carbonate of Soda enables the reducing agent to combine with the silver and give the desired deposit.

It is quite possible that when using the amount of soda the formula calls for, that a different brand of soda than that designated in the formula has been used. It is necessary to take into consideration the difference between the various brands of Carbonate of Soda. Two brands of Carbonate of Soda might test the same when dissolved in water, but one would have a much stronger alkaline reaction than the other. Many brands of soda contain large quantities of Bi-carbonate which, though helping to raise the hydrometer test, does not have an accelerating action in the developer and. in fact, would have no more relation to the process of development than so much sugar or neutral chemical dissolved with the Carbonate.

The hydrometer shows the amount of solids in solution and has no value unless the strength of the chemical is known. For this reason Kodak Tested Carbonate of Soda, which contains 98.2% pure Carbonate, would not weigh more nor test higher than an equal quantity of a Carbonate containing impurities, but the difference in developing action would be unmistakably apparent in the negative. When mixing chemicals in accordance with any given formula, the kind of chemicals designated should not be overlooked.

There is probably no chemical varying so much in strength as Carbonate of Soda of different brands. When using Carbonate in which there is an insufficient amount of alkali, the proportion must necessarily be increased to produce the same action. It is, therefore, important when mixing up developers where Eastman sodas are specified that these sodas be used.

The increasing popularity of Kodak Tested Sodas is due to their being of uniform strength and action. With their use it is possible to be absolutely sure of the degree of alkalinity of the developer. They are the most satisfactory to use from the standpoint of economy as well as certainty of results.