284 EARLE B. PHELPS 



cases it must be assumed that certain organic compounds are formed. 

 If such compounds are found upon investigation to be non-toxic, or 

 to have a lower toxic value than the original copper salt, this fact may 

 throw some light upon the nature of the toxic action itself. 



It was the purpose of the present investigation to study the germi- 

 cidal action of copper sulphate upon the typhoid organism in distilled 

 water and in the presence of certain organic compounds. Organic 

 substances were selected which would not in any case precipitate the 

 copper, and which, according to the chemical evidence, do not form 

 any direct union with it. This does not preclude the formation of a 

 ''physiological compound," as denned by Stiles and Beers (1905), 

 namely, a compound which is not readily detectible by chemical 

 means, but which possesses characteristic physiological properties. 

 For this purpose dextrose and peptone were used. The organic 

 matter occurring naturally in Boston tap water, a colored surface 

 water, was also studied. 



METHODS. 



Preparation oj copper sulphate. The copper sulphate used was 

 carefully prepared to assure a pure product. In particular was it 

 desired to obtain salt free from ammonia, since there is reason to believe 

 that the double or cuprammonium salt will have a distinctly different 

 toxic effect from that of the simple copper salt. Some "C. P." cop- 

 per sulphate crystals were dissolved in water, making about a 10 per 

 cent solution. To this solution a small amount of Na 2 CO 3 was added, 

 and the solution was boiled for some time to expel the ammonia. It 

 was then acidified and submitted to electrolysis with a small current, 

 about o . 05 ampere, and a potential difference through the solution of 

 about one volt. Copper was deposited on the inside of a platinum 

 dish which served as a cathode. This deposit of copper was then 

 washed with ammonia-free water and redissolved in dilute sulphuric 

 acid by reversing the current. The product obtained by crystallizing 

 this solution was recrystallized from ammonia-free water to free it 

 from the last traces of acid. It was dried for several days over 

 calcium chloride and caustic potash. 



Preparation oj potassium sulphate. This salt was prepared by 

 twice recrystallizing the best Merck preparation from ammonia-free 

 water. 



