168 



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



solute on to a surface, takes place in Stage 1, so that it is obvious that this 

 stage can occur in the absence of free oxygen — that is, of oxygen other than 

 what may be still clinging to the silk surface. The final effect, namely, the 

 development of colour, is no part of the staining process, and is not an 

 indication that the surface of the silk has any special affinity for oxygen, or 

 is a place where oxidation is taking place. 



Such experiments as this, however, and similar ones, with gelatine, agar, 

 and the gel of silicic acid, leave the fundamental proposition, which seems to 

 be the basis of Unna's work, untouched, namely, that the condensation of a 

 basic substance with a high avidity for oxygen, such as the reduction 

 product, the leucobase of methylene blue, or of the fully oxidised coloured 

 body methylene blue, occurs either where oxidation is taking place or where 

 there is a condensation of oxygen. To disprove this contention it is 

 necessary to show that condensation may occur on to the surface of a body 

 already fully oxidised, and completely freed from the film of condensed 

 oxygen, which adheres so tenaciously to solid surfaces which have been 

 exposed to air. As is well known, a solution of a basic dye filtered through 

 a layer of sand is decolorised, the dye being condensed on to the sand 

 particles ; sand, therefore, was chosen. 



Experiments with Sand. 



The procedure was as follows : — About 2 inches of sand were packed in a 

 small combustion tube, having a pad of asbestos at one end to prevent the 

 sand from washing through, when the various solutions were passed through. 

 Hydrogen, prepared in a Kipp apparatus, was washed in water to remove 

 acid, passed through a strong solution of alkaline pyrogallate to remove 

 oxygen or traces of acid still remaining, and finally passed through a long 

 tower of calcium chloride to remove water. 



The apparatus used was similar to that used for silk, save that the 

 three-way tube was fixed on to a combustion tube which contained the sand. 

 The sand was heated to redness in a furnace, and the purified hydrogen 

 passed over it while it was in this condition. The heating was followed by 

 cooling, and this by heating again, still, of course, in a stream of hydrogen, 

 and this was followed by cooling once more in a stream of hydrogen. These 

 series of operations were carried on for three to four hours, so as completely to 

 burn off the oxygen.* After the sand had cooled in the atmosphere of 

 hydrogen, rongalit white solution, freed from oxygen by passing nitrogen 

 gas through it for six hours, was allowed to flow in. It was allowed to stay 



* Compare " Contact Electricity," F. M. Spiers, ' Phil. Mag.,' 5th ser., vol. 49, Part 1 

 (1900). 



