DARKROOMS AND DARKROOM PRACTICE 



571 



Accuracy in Conipoundi?ig Solutions. — Errors or inaccuracies iu making solutions 

 should not be greater than a few per cent. If the photographer wishes to convert a 

 formula written in metric units to avoirdupois, he will often "round off" the quantities 

 to get convenient values. Care must be taken in this rounding off to see that cumula- 

 tive errors are not caused. For example, the ratio between inetol and hydroquinone 

 in any MQ developer is important. In rounding off, if one uses a figure 3 per cent 

 low for metol and 3 per cent high for hydroquinone, the total error is 6 per cent, which 

 is about the limit that should be tolerated. Similar difficulties may arise in changing 

 the ratio between carbonate and sulphite in a solution. 



The following table will be useful in converting formulas from metric to avoirdupois 

 and vice versa. Other conversion factors and tables wUl be found in Appendix A. 



Table III. — Avoirdupois to Metric Weight 



In converting United States liquid to metric measure, remember that 1 gal. is 

 equal to 4 qt. or 8 pt. or 3.785 1.; that 1 oz. is 8 drams or 30 cc. (29.57 cc. actually); 

 that 1 qt. is approximately 1 1. (actually 946.3 cc). 



English formulas are frequently worked out for 40 oz. rather than in units of 16 oz. 

 (United States pints) or quarts. This is because 1 qt. in the British imperial liquid 

 measure is equal to 40 British fluid ounces. Therefore, to convert a 40-oz. solution 

 to a 32-oz. solution, multiply all ingredients in the 40-oz. formula by 0.8. Conversely, 

 to make up a 40-oz. solution from a 32 oz. formula, multiply the 32-oz. values by 1.25. 



Bibliography 



Periodicals: 



JouRDAN, Albert: Metol Poisoning, Am. Phot., July, 1935, p. 397. 



DlEFFENBACH, A. M.: Cooling Bath for Hot Weather Development, Am. Phot., July, 1935, p. 435. 

 Snodgrass, L. L.: Is Photography Your Hobby? (Darkrooms for the Amateur), Atn. Ho7ne, May, 1936. 

 Fink, D. G.: For Photographers Only (Description of an Electronic Darkroom Timer), Electronics, 



June, 1937. 

 Hertzberg, Robert: An Efficient Ventilator, Camera, July, 1937, p. 20. 



LooTENS, C. L.: Modern Motion Pictures Laboratory, J. Sac. Motion Picture Engrs., April, 1938, p. 363. 

 Smith, H. A.: Stainless Steel and Its Application to Photographic Processing Equipment, J. Soc. Motion 



Picture Engrs., April, 1938, p. 410. 



Books: 



"Supplies for the Graphic Arts," Eastman Kodak Co. 

 "Commercial Photo Finishing," Eastman Kodak Co. 

 "Fundamentals of Radiography," Eastman Kodak Co. 

 "Motion Picture Laboratory Practice," Eastman Kodak Co. 



