408 HANDBOOK OF PHOTOGRAPHY 



although quicker drying can be obtained by playing a draft of air over the materials 

 to be dried. If the air is heated, drying will be more rapid, but the temperature 

 should not exceed 90°F. 



While drying by forced air flow maj^ sometimes be advantageous, this method 

 tends to stir up the air more completely than normal drying and, in so doing, also 

 stirs up dust and dirt which may be deposited upon the film. The deposit of dust 

 particles on the film is particularly serious in the case of small negatives from which 

 enlarged prints are made. One means of minimizing this contamination by foreign 

 particles is to place the material to be dried in a w^ooden or metal frame or box which is 

 covered with a cloth of very fine mesh; sufficiently fine so as not to permit dust par- 

 ticles to pass through it. The air may then be blown over this box. While the use 

 of the fine mesh cloth will reduce the air circulation somewhat and thereby prolong the 

 drying time, none of the particles outside of the frame can be deposited upon the film. 

 By making the frame small enough to hold onl^'' the required number of negatives, the 

 amount of dust inside the frame can be minimized. 



Certain liquids having low vapor pressure so that thej^ evaporate readily may be 

 used to assist in rapid drying. Of these materials the most common and useful is 

 alcohol. After washing has been completed, the surface water is drained off, and the 

 negatives are immersed in alcohol.^ The negatives are allowed to remain in the 

 alcohol bath for a sufficiently long time for the alcohol to permeate the gelatin coating, 

 thereby replacing as much of the remaining water as possible. Ordinarily from 3 to 

 5 min. should be sufficient for this purpose, after which the negatives may be removed, 

 drained of their surface alcohol, and hung up to dr3^ If desired, much of the surface 

 alcohol may be removed by blotting with a soft cloth or viscose sponge, but in this 

 case care should be taken that lint deposits do not adhere to the negative. 



The rapidity with which such an alcohol-treated negative will dry depends upon 

 the degree to which air is circulated over the negative, the temperature and humidity 

 of the air, and the percentage of water in the alcohol. Water and alcohol are miscible 

 in all proportions, and as water is brought over to the alcohol bath from the final water 

 wash bath, the alcohol becomes more and more diluted and loses some of its eff'ective- 

 ness as a rapid drying agent. 



Sometimes it is found that a faint opalescent deposit appears on the negative 

 which has been rinsed in alcohol. This is likely to occur if poor grades of alcohol 

 (such as rubbing alcohol) are used but may usually be removed by rubbing the surface 

 of the dried negative with a soft cloth or lens tissue. If a negative has not been 

 sufficiently fixed, it will assume a white opaloid or white appearance when immersed 

 in the alcohol bath. The removal of this opalescence may be accomplished by washing 

 the negative in clear water and then returning it to the fixing bath for more thorough 

 and complete fixation. 



As alcohol is a solvent for the support sometimes used for certain films, it should 

 not be employed with cellulose nitrate films. In this case drying may be hastened by 

 immersing the film in a 40 per cent solution of formalin or formaldehyde for 5 min. 

 following the final wash in clear water, after which the negative should be dried in a 

 current of air at as high a temperature as is consistent with prevention of injury to 

 the supporting base. Such procedure has considerable potentialities of damage to 

 the negative, especially if attempted by the inexperienced worker and is recommended 

 for use only in emergencies. 



Quick drying can also be carried out by using ether instead of alcohol as the final 

 wash bath. Ether and its fumes are highly inflammable and operations with this 



' The use of an alcohol bath is suitable for glass plates and film materials made of cellulose acetate, 

 as well as printing papers. Cellulose nitrate films are soluble in alcohol so that such negatives cannot be 

 washed in alcohol. From 10 to 20 per cent water should be added to alcohol for this bath. 



