820 



EXPLORATION GEOPHYSICS 



wool) prevents rapid temperature variations. An ice-pack in summer 

 and a hot water bath in winter are used to adjust the temperature at the 

 beginning of a day. Only minor attention is required thereafter to main- 

 tain it. Records are developed in accordance with time-temperature 

 charts, with consideration given to the age of the developer. 



After it has been developed, the record should be washed in a stop 

 solution consisting of Ij^ ounces of 28% acetic acid dissolved in 32 

 ounces of water. Fixation of the record is accomplished by immersing 

 it in a solution of sodium thiosulphate (trade term "hypo") which re- 

 moves the unexposed silver. Prepared packages of this material, with the 

 necessary hardener, are available from all manufacturers of paper. Fixa- 

 tion is usually complete within three to five minutes. After sufficient 

 fixing, the film should be immersed in a fresh water bath to insure a per- 

 manent, non-fading, and non-stained record. 



Although it is often neglected, proper washing of the records is one 

 of the important steps in the processing. The removal of soluble chem- 

 icals remaining in the paper after the fixing operation can only be ac- 

 complished by thorough washing in clean water. If it is inconvenient 

 to supply sufficient water for each batch of records, the films should be 

 left in the water bath until the return of the operators to headquarters. 

 The records can then be placed in a large container (the bath tub may 



be convenient) with cool fresh 

 /.S running water and washed for 

 '^^ about thirty minutes, and then 

 dried. 



During the developing, fixing, 

 and washing steps, the record 

 must be carefully moved or the 

 fluid agitated to insure uniform 

 exposure to the solution of all 

 parts of the record. 



Caution must be exercised to 



prevent the stop bath and hypo 



from splashing or dripping into 



the developer. Among the best 



containers for solutions are glass 



(deep Pyrex cooking pans), glazed earthenware, or stainless steel jars. 



The containers should be provided with sealing lids to prevent "slopping" 



of the solutions when the truck is moved during the day. 



Figure 504 shows a simple but effective assembly for field use where 

 a limited number of records is to be developed. The jars are ordinary 

 earthenware thermally-insulated jugs with large open mouth, of the type 

 employed for food. These jars are provided with tight-fitting rubber- 

 sealed lids that preserve the solutions and prevent splashing while the 

 truck is in motion between set-ups. The lower ends of the jars are set into 



Fig. 504. — Processing assembly for photographic 

 records, a, developer; b, stop bath; c, fixing bath; 

 d, fresh water; e, rubber-sealed lids; f, absorbent 

 paper toweling. 



