We merely want to warn you to warn your assistants, especially the new ones, of the great importance of correct temperature of solutions. Buy a thermometer or two and insist on their being used and explain why it is important.

All photographic chemical reactions slow up as their temperature is reduced and proceed more rapidly as their temperature is increased. If this were the sole result of changes in temperature, the danger would not be great. But there is a change in chemical action as well as in the speed of action, with changes in temperature, and this has led manufacturers to determine the temperature at which solutions will produce the best results and to recommend that these temperatures be kept constant.

The photographic chemist numerically measures the extent to which different chemical reactions are stimulated by a given rise in temperature and the result is known as the "temperature coefficient." The greater the effect of temperature on a chemical reaction the greater is its temperature coefficient.

Specify C. K. Co. Tested Chemicals.

Temperature StudioLightMagazine1918 250


By Jerome Chircosta Cleveland, O.

This information is very important to the laboratory worker as the effect of temperature varies very much with different developing agents. For example, the effect of temperature on Elon is very small, while on Hydrochinon it is very great. A developer made up of Elon and Hydrochinon may have these two agents balanced to a nicety for use at a normal temperature (65°). Reduce the temperature and the Hydrochinon action will slow up, while the Elon action will be little affected, so the developer will behave as though it contained an excess of Elon. At high temperature the Hydrochinon is increased in its activity far more than the Elon and the result is reversed.

This explains why prints from the same negative, on the same paper, developed with the same developer may lack uniformity of contrast. Of course, the paper usually gets the blame, but it is rarely at fault. You may find your own printer using developer at temperatures varying as much as fifteen or eighteen degrees from time to time, and results are bound to vary.

Just here it might be well to state that an accelerator such as carbonate of soda, gives the developing agent its energy as well as prepares the gelatine for the developer to enter its pores, but an increase in carbonate will not make up for low temperature of the solution, will cause fog and will often cause a gelatine emulsion to frill or blister.

The effect of a low temperature developer on plates or film is that of under-development and should be corrected by raising the temperature of the solution. The same applies to the developers for papers.

A similar principle applies to the fogging produced by developers. All developers will produce chemical fog if development is continued for a long enough time. But fog is produced much more quickly as the temperature of the developer is increased. Fog reaction is different to development reaction and has a temperature coefficient that is much higher. A developer which will develop a material to a good density with practically no trace of fog at normal temperature, may produce very bad fog if the temperature is raised ten degrees.

Aside from the troubles that may be encountered if developing temperatures are too high or too low, there are like dangers to be encountered in fixing. At too high temperatures there may be staining, softening, frilling or reticulation, and if the temperature is too low, fixing will be slow and there is the chance of insufficient fixation.

A radical difference between the temperature of the developer and the fixing bath will also cause trouble, so it is a wise precaution to personally see that solutions are kept at somewhere near normal temperatures and by so doing, avoid a great deal of unnecessary trouble.

When he comes home - there should be a new portrait to record the event. Make the appointment for him.

Temperature StudioLightMagazine1918 252


Line cut No. 258. Price, 50 cents.