Microchemical Test for the Oxygen Place in Tissues. 169 



hi the tube for one or two minutes, after which it was washed through by a 

 stream of nitrogen water. 



The sand was then treated in one of two ways — it was either kept in the tube, 

 the two ends of which were open to the air, or it was washed through by the- 

 nitrogen water on to filter paper. The object of the second procedure was to 

 eliminate the possibility that it might be only the solution of rongalit white 

 trapped between the sand grains that underwent oxidation, the methylene 

 blue so produced being taken up by the sand. If any such trapped solution 

 exists, it is rapidly taken up by the filter paper. 



The results which the first method gave are interesting. It was noticed 

 that no blueing occurs for a considerable time, although the tube has been 

 full of air. That is to say, the hydrogen which has replaced the oxygen on 

 the surface of the sand continues in possession of that surface for some time 

 after it is brought into the presence of oxygen. A similar condition is met 

 with in the case of iron ; if the oxygen which is normally condensed on the 

 surface of the iron is completely replaced by a layer of hydrogen, the 

 potential difference between the iron and another metal plate is changed. 

 When the iron is brought into the presence of air the reversion to the 

 original potential difference is very slow, thus showing that the hydrogen is 

 only slowly displaced from the surface of the iron.* 



Details of an Experiment. 



3.10. Sand heated to redness and hydrogen passed through. 

 3.40. Allowed to cool in a stream of hydrogen. 

 3.50. Again heated to redness in hydrogen stream. 

 5.0. Allowed to cool in stream of hydrogen. 



5.15. Eongalit white solution passed through and allowed to remain in 

 contact with the sand for one minute. There was no appearance 

 of any colour at all.f Nitrogen water was then passed through 

 for three minutes : again there was no sign of colour in the sand. 

 The nitrogen water was then driven through by a stream of 

 nitrogen gas. 



5.25. Tube opened to the air and shaken to disturb the gas inside the tube. 

 5.40. Xo colour. 

 6.0. Xo colour. 



6.30. Slight blue colour beginning to develop. 



Proni this time onwards the colour gradually developed and deepened, 

 till at 12.0 it had become dark blue. 



* Loc. cit., p. 2. 



t Ordinary sand when placed in rongalit solution turns a green-blue colour. 



