Thiosulphate by Certain Bacteria in Pure Culture. 443 



ammonium sulphate gelatine plates were similarly oxidised, and other 

 experiments have been conducted which confirm the above results. 



The following is a typical example of the chemical results obtained : — 



Eesults in parts per 100,000. 





Oxygen absorbed in 

 three minutes from 

 acid permanganate. 



Eeaction with 

 mercurous nitrate. 



Inoculated solution after 21 days' incubation 

 at 20° C. 



Solution of control experiment after 21 days' 

 incubation at 20° C. 



1 00 

 28 -80* 



White ppt. 

 Black ppt. 



* Equivalent to 83 "8 parts Ka.jS 2 3 per 100,000. 



That the thiosulphate is bacterially oxidised to sulphate and that the 

 change is not a simple decomposition due to the formation of acid by the 

 organism seems evident from the fact that (1) there is no deposition of free 

 sulphur, (2) the final solutions do not absorb appreciable amounts of oxygen 

 from acid permanganate, this excludes the presence of thionic acids. 



The following are comparative results obtained with three solutions, to one 

 of which had been added before incubation 1 c.c. of normal sulphuric acid, 

 thereby making the solution decidedly acid to methyl orange : — 



Eesults in parts per 100,000. 





Oxygen absorbed in Eea ction with 

 three minutes from i .. . 



. , . mercurous nitrate, 

 acid permanganate. 



Remarks. 



1. Inoculated solution after 21 days' 



incubation at 20° C. 



2. Solution of control after 21 days' 



incubation at 20° C. 



3. Solution made decidedly acid to 



methyl orange prior to 21 days' 

 incubation at 20° C. 



1-80 

 21 -00* 

 14 -60 



White ppt. 



Black ppt. 



Yellow ppt. 

 (thionic acids). 



SUght 

 turbidity. 



Clear 

 solution. 

 Deposit of 

 sulphur. 



* Equivalent to 61 parts Na ; S 2 3 per 100,000. 



The organism is apparently able to live in slightly acid solutions, although 

 prolonged contact with free acid appears seriously to impair its activity and 

 growth. 



Further experiments are in progress relating to the morphology and 

 classification of the organism, which appears to be one hitherto unknown, 

 and to its effect on other sulphur compounds, e.g. tetrathionate. 



