578 



by a special bottle which allows the collecting of samples and the in- 

 troduction of the chemicals without exposing the samples to air during 

 the operation. 



The apparatus shown in the accompanying figure is composed of a 

 bottle having an inlet, a, at bottom and an outlet, b, at top. When the 

 bottle is filled the inlet is clamped off at c. The manganous solution is 

 introduced through the burette d and the potassium iodide-alkali solu- 

 tion through the burette c. The burettes d and e are supplied with a 

 two-way stop-cock at /. The displaced water is allowed to pass out at 

 the outlet b, which is kept open to equalize the pressure. The acid 

 solution is introduced through the burette d, thus avoiding any action 

 of a strong acid on the potassium iodide of the potassium iodide- 

 alkali solution. A 200 c.c. pipette is used to draw a sample for 

 titration, thus avoiding agitation of sample in presence of air. Cor- 

 rection for error due to the introduction of chemicals can be calcu- 

 lated from the per cent, of collection used for titration with sodium 

 thiosulphate, and the oxygen content of the water can be calculated 

 directly. In lieu of the simple pipette for drawing off sample of water 

 for titration, the device described by Hyman L. Shoub* may be sub- 

 stituted. 



A modification of this bottle is also very useful for work with 

 hydrogen sulphide, sulphur dioxide, carbon dioxide, and other gases 

 when exclusion from the air is essential. 



I wish to thank Mr. Carl F. Miller and Mr. Paul Anders, of the 

 Chemical Laboratory of the University of Illinois, for making this 

 apparatus available. 



•Hygienic Lab. Bull. 9G, U. S. P. H. S. Aug., 1914. 



