32 



IVAN C. HALL 



The importance in such observations of having a sufficient 

 quantity of test solution is shown in the following experiment 

 which offers a comparison of the results with equal ratios but 

 differing absolute quantities of test solution and seal. 



The liquid test solution was the usual 2 per cent glucose, with 

 n/500 NaOH, and 1:100,000 methylene blue; the agar test 

 solution was 2 per cent agar with n/1 NaOH and 1:100,000 

 methylene blue; the seal was vaseline. The mixtures were made 

 in tubes of 10 cm. diameter and heated in a boiUng water bath 

 for a few minutes to decolorize. They were allowed to stand 

 overnight at room temperature and then examined for recolor- 

 ation. The results appear in table 5. 



TABLE 5 



Relation between absolute and proportional quantities of test solution and seal 



VASELINE SOLUTION 



VASELINE SOLUTION 



Liquid test solution 



The logical explanation of this result appears to He in the 

 assumption that sufficient oxygen or carbon dioxide is retained 

 in the seal to recolor a small amount of test fluid pre^dous to 

 setting of the seal but not sufficient to recolor a larger amount. 



Boiling' an agar solution under 3 cm. of oil, in a water bath, 

 heating to 25 pounds steam pressure (267°C.) in the autoclave 

 for twenty minutes, or layering the separately heated oil and 

 agar solutions, made onty a slight difference in the rate of return 

 of color at the oil-agar surface, which is almost as rapid as with- 

 out the oil. 



