12 IVAN C. HALL 



On boiling five minutes all were decolorized above and below 

 except tube 4. TJiis experiment thus illustrates not only the 

 point just mentioned but also our frequent observation that 

 very weakly alkaline solutions are likely to fail to decolorize if 

 allowed to stand exposed to the air long before use, probably 

 owing to neutralization by CO?. This is a point to which we 

 shall return. 



As to variations in dye content with n/1000 NaOH and 1 per 

 cent glucose, 1 : 1000 and 1 : 10,000 methylene blue failed to 

 decolorize in this particular experiment while solutions contain- 

 ing 1:100,000 did so. The weaker the concentration of dye, 

 the less alkali is required. 



With N/1000 NaOH and 1:10,000 methylene blue variations 

 in glucose from 0.15 to 20 per cent appeared to make little or 

 no difference in decolorization, yet further dilution and variations 

 in alkahnity and dye content showed distinct effects, to which 

 reference will now be made for it is apparent that the three 

 reagents necessaiy in a test for the decolorization of methylene 

 blue by heating bear a definite quantitative relation, one to 

 another. Briefly, the amount of alkali required bears an inverse 

 relation to that of glucose but the necessary amounts of these 

 two reagents bear a direct relation to that of methylene blue. 

 The more alkali the less glucose is required and vice versa, but 

 the more methylene blue the more glucose or alkali is required. 

 Those relations are best displayed in the following experiment: 



For the purpose of this and several similar experiments a 

 copper water bath with a support providing for 10 rows of 10 

 perforations each to hold test tubes was used. The tubes were 

 of uniform size as to length and bore; they were carefully cleaned 

 and placed in the support in rows corresponding to the record 

 marks of table 2, one tube for each mark. To each were first 

 added 7 cc. neutral distilled water and 1 cc. of an aqueous meth- 

 ylene blue solution 10 times the strength required in that particu- 

 lar section of the experiment. Solutions 10 times the strength 

 of glucose required in each of the vertical rows and of sodium 

 hydroxide in each of the horizontal rows were prepared and of 

 these 1 cc. each was added to each tube in the test. In such 



