246 Mr.Weston on the Reciprocal Action 



Hot Solution. Cold Solution, 



Sulphuret of Potash. 



4. Lessens colour. 4. Lessens colour. 



Liquid Chlorine, 



5. Removes colour, by yf***^ bring- 5. Removes colour. 

 \Dg it back to blue. 



Oxygen Gas. 



6. Passed through the solution 6. Surface rendered reddish 

 did not increase the colour. blue. The whole a lighter green, 



with a precipitate of what appear- 

 ed to be indigo. 



We see, in No. 1, that the indigo is first deoxygenized, and 

 rendered green, and that it then regains its oxygen, and be- 

 comes blue, unless the atmosphere be excluded ; and, there- 

 fore, it follows, the same laws which govern its solution in water, 

 and so far, it confessedly changes its colour by the absorption 

 of oxygen. 



Again, we see that the crimson is affected by the deoxygen- 

 izing tests equally with the cold solution, and consequently the 

 substance contained in both these solutions is, I conclude, ana- 

 logous in its nature. 



We also see by No. 6, that oxygen, without any elevation 

 of the temperature of the menstruum, can produce the reddish 

 \Aue ; and lastly, by No. 5, we see that chlorine, in combining 

 with the oxygen, and abstracting it from the indigo in solution, 

 makes the compound, as it were, to retrace its steps, and re- 

 duces it from the crimson <o the blue. The collective evi- 

 dence, therefore, of these experiments seems to prove, that no 

 decomposition of the indigo has taken place by the application 

 of heat, and that the carmine, or crimson colour, has resulted 

 from the extraordinary quantify of oxygen which the favourable 

 circumstances attending the solution has enabled it to receive. 

 One remarkable circumstance, suggested by experiment 

 No. 3, must here be noticed. It is there seen, that alcohol 

 removed both the crimson and the green colour, and yet alcohol 

 has no influence whatever on the blue indigo or its crystals. 

 The capability, therefore, of alcohol as a solvent of indigo. 



