22 Mr, Tomlinson on [July 



solution on the mercury the accidental blue was obtained 

 very perfectly. The surface of the mercury, however, soon 

 tarnishes. 



5. I have employed several green solutions, and find that 

 one to succeed which is obtained by the addition of alcohol 

 in sulphuric acid to a solution of bichromate of potassa. 

 This compound, (an impure sulphate of chromium) is of a 

 dark and decided green, and yields a red accidental colour. 

 With a lighted taper, other lights being extinguished, a 

 beautiful complementary reflection is obtained, and the 

 surface of the liquid is interspersed with red rays. 



6. The true accidental colour of green is violet-red, so 

 that the last experiment did not satisfy me. To produce 

 this accidental colour, a grass-green solution must be 

 employed, which, I find, may be formed by the addition 

 of the bright blue solution of nitrate of copper (7.) to the 

 red solution of bichromate of potassa. A fine complemen- 

 tary colour is obtained from the solution on mercury, but 

 an amalgam is soon formed on the surface of the metal, 

 which prevents further observation. If it be required to 

 repeat the experiment the amalgam can be easily moved 

 aside with a flat piece of glass.'* 



7. For a blue, I employed nitrate of copper, the filtered 

 residual solution from the retort, after making binoxide of 

 nitrogen. This bright blue solution on mercury yielded a 

 fine orange red. 



The nitrate of copper of commerce I have often found to 

 consist of a confused mass of green crystals. Practically, 

 I find, that the bright blue solution, when quickly evapo- 

 rated, yields a confused green crystallization ; but by careful 

 evaporation, bright blue crystals, the colour of the solution, 

 are obtained. The green salt probably contains less water 

 than the blue, and certainly does not deliquesce so soon ; 

 it is of the colour of the subsalt, but distinguished from that 

 by being soluble in water. The solution of the latter is of 

 a greenish-blue, yielding a reddish accident on mercury. 



8. I obtained a violet solution by means of archil f lichen 

 roccellaj, and the accident, a delicate yellowish green, was 

 immediately obtained. A few drops of liquor ammonige 



• I shall have occasion to refer to this amalgam in my next paper on Visible 

 Vibration, respecting its appearances during and imioediately after the vibration 

 •f the glass. 



