388 HANDBOOK OF PHOTOGRAPHY 



The composition of fixing baths recommended for various purposes is given in 

 Table II. No effort has been made to include all the fixing baths which have been 

 published from time to time, but the solutions given are representative of current 

 practice. The baths are divided into three main groups, according to whether they 

 are plain fixing baths, acid nonhardening fixing baths, or acid fixing baths. Under 

 these main groupings, the baths are further classified according to the use or special 

 property for which they are recommended. 



The plain fixing baths, 1 and 2, are simple nonhardening baths. They are suitable 

 for use where the films are ^^■ashed in a stop bath or in fresh water between develop- 

 ment and fixing. The baths differ only in concentration of hypo, and the two con- 

 centrations given represent approximately the extreme concentrations encountered in 

 practice for baths of this type. 



Baths 3 to 6 inclusive are acid nonhardening baths which are suitable for plates, 

 films, or prints. 



Baths 7 and 8 are recommended for films, while bath 9 has been suggested as being 

 especial! j^ suitable for slides. The sodium sulphite is first dissolved in about 50 cc. 

 and the hydrochloric acid is added. The hypo is dissolved in about 900 cc. of 

 water, and, when it has completely dissolved, the first solution is added to the hypo 

 solution and the volume broiight up to 1 1. 



Baths 10 and 11 have been recommended for prints where a nonhardening bath is 

 suitable. 



Acid hardening fixing baths (12 andJoeyond) are the most suitable for general use 

 as the processes of fixing and hardening are combined in a single bath operation. The 

 first three baths under this classification are suitable for films, plates, or papers. 

 Bath 12 is a potassium alum bath. Bath 17 keeps indefinitely before using and there- 

 fore can be made up in advance of use; it can also be used repeatedly. Since it becomes 

 gradually alkaline with the addition of developer to the fixing solution, the bath should 

 be discarded when it becomes frothy. One pint should fix fifty 4- by 5-in. prints. 



Although listed here as especially suitable for motion-picture work. No. 15 is an 

 acid hardening bath suitable for all professional films and plates. Bath 16 has the 

 advantage of having the lowest effect on reduction of the silver image of a wide number 

 of fixing solutions investigated by Russell and Crabtree (see page 378). Bath 18 is a 

 chrome alum fixing bath for professional plates and films, as well as for motion-picture 

 work. Since chrome alum baths often lose their hardening properties within a few 

 days after their preparation, either with use or without, a fresh bath should be pre- 

 pared immediately before using. There is a tendency for scum to form in old baths, 

 but this scum may be removed by swabbing the surface of the film with cotton. For 

 bath 20 the hypo should be dissolved in one-half the required volume of water. The 

 sodium sulphite, acetic acid, boric acid, and potassium alum should then be added 

 in the order given here, after which the volume of solution is brought up to 1 1. by 

 adding the proper amount of water. This bath contains a minimum amount of sul- 

 phite, so that sulphurization will not occur within a period of 3 or 4 weeks when the 

 temperature is 70°F. If the bath temperature rises above 70°F., double the amount of 

 sulphite indicated may be used. Bath 21 is a suitable chrome alum fixing bath for 

 motion-picture work. It does not harden the film excessively but maintains its 

 hardening properties on keeping. The bath does not sludge with the addition of a 

 relatively large amount of developing solution and, if the temperature does not exceed 

 70°F., will not sulphurize in less than 4 weeks. 



Bath 22, suitable for paper prints, has an exceedingly long hardening sludge life, 

 and produces considerable hardening of paper prints. This borax bath has been found 

 to have a hardening life approximately four times that of bath 17 and a sludge life five 

 times as long. 



