28 



IVAN C. HALL 



oil that the color returns to alkaline glucose methylene blue 

 solution decolorized under varying depths of oil by heating in 

 a boiling water bath almost as soon as without the oil. The 

 following instance illustrates this point. Two per cent glucose 

 (Pfanstiehl) with n/500 NaOH and 1:100,000 methylene blue 

 (Griibler) in aqueous solution was placed in equal depth (3 cm.) 

 in similar culture tubes of | inch diameter and covered to the 

 depths noted with "Fulmor" oil, a white neutral mineral oil 

 prepared by the Fuller Morrison Company of Chicago; a con- 

 stricted tube with the same dye solution and marble seal was 

 included for a control. It should be noted that the diameter 

 of this tube was about twice, and the surface exposure of liquid 

 therefore 4 times, that of the other, thus offering even greater 

 opportunities for rapid recoloration, which was observed above 

 the seal. All were decolorized throughout by heating two 

 minutes in the boihng water bath and readings made as follows 

 on the removal therefrom. 



* Not boiled with other tubes — still colorless below after six days. 



This representative experiment indicates that oil is much less 

 efficacious than sometimes assumed as a means of oxygen exclu- 

 sion. The progressive ease of repeated decolorization in relation 

 to depth of oil suggests that carbon dioxide is excluded somewhat 

 better but one must not lose sight of the fact that the maximum 

 depth of oil in this experiment is much greater than ordinarily 

 used. 



