172 



Mr. A. N. Drury. The Validity of the 



heated for three hours and one hour respectively and were allowed to cool in 

 their respective gases. The sand was then turned into the methylene blue, 

 the hydrogen sand into the nitrogen methylene blue, the air sand into the 

 air methylene blue. 



After they had remained in the methylene blue for equal periods of time, 

 the solution was decanted off, and the sand carefully dried, the intensity of 

 blueing of the sand showing a very appreciable difference even to the eye. 

 The solutions of methylene blue were compared by means of the colorimeter 

 with the original solution. The sand was heated strongly to vaporise the 

 methylene blue on its surface, and was then weighed. 



Account of an Experiment. — Sand was heated in a hydrogen atmosphere for 

 three hours, and cooled in an atmosphere of that gas ; it was then put into 

 nitrogen methylene blue solution for five minutes. The sand was decanted 

 off and was compared with the original methylene blue solution by means of 

 the colorimeter. The sand was dried, heated to volatilise the methylene 

 blue, and weighed. 



A similar quantity of sand was likewise heated in a stream of air for three 

 hours, cooled and put into ordinary methylene blue solution of the same 

 strength for five minutes, decanted off and compared with the original solution 

 by means of the colorimeter. The sand was dried, heated, and weighed. The 

 same volume of solution was used in both cases : — 



Wt. Sol. Orig. sol. 



A. — Sand heated in hydrogen T75 0'8 - 5 



B. — , „ air 1-03 0"75 0'5 



The result can be represented as columns of methylene blue solutions on 

 the same base and containing the same amount of dye. 



Original solution 5 



Solution A 7-5 



Solution B 12-5 



This experiment shows that the gas condensed on the surface plays an 

 important part in the depth of staining which the surface undergoes. An 

 explanation is, perhaps, to be found in the alteration of the electrical potential 

 of the surface. 



The Effect of Certain Chemical Substances on the Amount of Methylene Blue 



Condensation on Sand. 



In the following experiments the sand was shaken up with the substance 

 to be tested, and washed in water. The methylene blue solution was then 



