170 



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



The method of spreading the sand on to dry filter paper gave similar 

 results. 



1.30. Sand heated to redness, stream of hydrogen passed over. 



2.0. Sand allowed to cool in hydrogen. 



2.10. Sand again heated in hydrogen. 



2.40. Sand allowed to cool in hydrogen. 



2.50. Sand again heated in hydrogen. 



3.20. Sand allowed to cool in hydrogen. 



3.30. Eongalit white solution allowed to flow in and to remain in tube 

 for one minute. This is followed by a stream of nitrogen water. 

 There was no sign of colour during these two stages. 



3.45. Sand washed out on to filter paper ; no colour. 



4.0. Slight blue-green tinge through the sand. 



5.15. Sand had become much deeper blue, the intensity of which continued 

 to increase for some hours. 



This experiment agrees with the former in every particular, except in the 

 time taken for the first appearance of the blue colour. This is a difference 

 rather to be expected than otherwise, as in the washing out on to the filter 

 paper the surface would be very much disturbed, and consequently the 

 condensed hydrogen would be more rapidly displaced. 



That the oxygen-free surface clings tenaciously to the rongalit white 

 condensed on to it appears from an experiment carried out in the same way 

 as the preceding. The sand was freed from oxygen, and then the oxygen-free 

 rongalit-white solution was passed over for one minute. After this the 

 nitrogen water was allowed to flow through until the water as it emerged con- 

 tained only very minute traces of methylene white. The sand inside the tube 

 was then exposed to air on filter paper, and it developed a quite appreciable 

 blue colour. There is thus no doubt that sand freed entirely from oxygen 

 not only condenses methylene white on to its surface, but also holds it with 

 a certain degree of pertinacity. 



Experiments on the Effects of the Gases condensed on the Surface on the Condensa- 

 tion of Methylene Blue. 



1. Oxygen. — A small combustion tube was filled with two inches of sand, 

 having at one end a plug of asbestos to prevent the sand from being moved 

 by the solution as it passed through. 



Through this tube a solution of methylene blue was allowed to flow by 

 gravity. The effluent was at first colourless, but with lapse of time as the 



