PRODUCTION OF HYDROGEN SULPHIDE 235 



EXPERIMENTAL WORK 



The application of hydrogen sulphide formation to water analysis 



Experiments were undertaken to ascertain the delicacy and 

 reliability of the hydrogen sulphide test used by Redfield to de- 

 termine the potability of water. 



The medium used was that suggested by Redfield with minor 

 modifications. Sodium chloride was substituted for potassium 

 chloride, and instead of the special flasks which Redfield employed, 

 Erlenmeyer flasks of 150 cc. capacity and made of Pyrex glass 

 were used. One-half per cent sodium chloride was added to all 

 media containing peptone because it seemed to produce a clearer 

 medium. Difco peptone made by the Digestive Ferments Com- 

 pany was substituted for Witte peptone since the latter is not now 

 obtainable. Ten cubic centimeters of the medium were placed in 

 each flask and autoclaved for ten minutes at 15 pounds pressure. 

 A strip of filter paper 50 mm. long and 3 mm in width was sus- 

 pended in the mouth of the flask in such a manner that approxi- 

 mately 30 mm. of the strip was exposed. The filter paper had 

 been moistened in a 10 per cent solution of neutral lead acetate, 

 and sterilized in the autoclave for fifteen minutes at 15 pounds 

 pressure. It was necessary to sterilize the lead acetate paper 

 separately because it was found that some blackening occurred 

 when the medium was autoclaved, due probably to a slight 

 hydrolysis of the peptone, since steam at the pressure of the 

 autoclave ionizes more than at atmospheric pressure. 



One gram of the feces under examination was weighed out. 

 This merely served as a convenient amount from which to make 

 dilutions since of course the moisture, bacterial content and resi- 

 due varied enormously in the different samples. A 90 cc. por- 

 tion of each dilution studied was placed in one of the Erlenmeyer 

 flasks and incubated aerobically at 37°C. The approximate 

 number of millimeters of lead acetate paper blackened was re- 

 corded at the end of twenty-four hours, forty-eight hours, seven- 

 ty-two hours, and seven days. The method was of course, only 

 approximate, but all conditions were kept as nearly identical as 



