Sir W. Crookes. 



An addition to the apparatus was made, a supplementary tube 

 sealed on containing a grain of corrosive sublimate. This was used as 

 being non-volatile at the ordinary temperature, but easily vaporised by 

 heat. The experiment last described was continued, and immediately 

 sifter the phosphoric blue edge appeared fresh hydrogen was let in and 

 exhaustion continued till the faint blue was eliminated. The mercury 

 salt was then heated, when immediately a rich blue edging appeared 

 on the face of each pink stratification and the yellow lines of mercury 

 shone out distinctly. Mercury blue is of a fuller colour than that of 

 the phosphoric blue. 



S\ 





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Altering the Colour of Stratifications. 



In the 'British Association Reports' for 1865 (Abstracts, p. 15), 

 Mr. Gassiot describes the changes produced in the colours of the 

 stratifications by introducing a water resistance in series with the 

 vacuum tube. Having shown that the blue components of 

 FIG. 6. the stratifications are due to the presence of a trace of 

 mercury with the hydrogen, experiments were commenced 

 to ascertain what difference in the strength of the induced 

 current would be necessary to alter the relative intensities 

 of the pink and blue strata. Accordingly, I fitted up a 

 resistance, shown in fig. 6, consisting of a glass tube, A A, 

 3 feet long and inch diameter nearly filled with distilled 

 water. Through a cork, B, at the upper end of the tube a 

 copper wire, C C, passes, and by raising or lowering the 

 wire either the whole resistance of the water or any fraction 

 of it can be thrown into the circuit. The upper part of the 

 wire is connected with one pole of the coil and the water 

 is connected with the other pole by means of a small 

 platinum wire sealed through the bottom of the tube. 



The wire was pushed down until it touched the platinum 

 at the bottom, thus cutting out the water resistance. The 

 strength of hammer-spring and the exhaustion were 

 arranged to show good pink and blue discs. The wire was 

 then gradually withdrawn, when the blue components 

 gradually faded, and at a resistance of 6 inches of water the 

 stratifications were all pink. Spectroscopic examination 

 showed that in the parti-coloured state mercury was 

 strongly present in all the blue components, together with 

 the C hydrogen line ; the mercury spectrum, however, 

 being in excess. But when the water resistance was put in, 

 and the buttons were all pink, mercury was still to be 

 detected, but the hydrogen spectrum was more prominent. 

 The green line of mercury was always the first to appear, 



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