1st. Mercury--gold color. " Copper slightly darkened. 2nd. Mercury--blue. " Copper dark red. 3rd. Mercury--green on some parts. " Copper white.
After this the copper underwent its usual changes of color on prolonging the action of the vapor of bromine, but the color of the mercury suffered no further change.
Mercury--a slight film. Copper no alteration of color. Mercury--deep gold color. Copper deep red on some parts, blue on others. Mercury--red tinged with blue. Copper blue, white. Mercury--blue. Copper same as before.
"With respect to the bromide and chloride of mercury, it is necessary to view them obliquely in order to perceive all the changes of color they undergo; for if looked at perpendicularly, there is seen on both a dull uneven film of white which reflects none of the above colors: consequently, to avoid any error, the copper must be inspected under the same angle.
Silver--pale gold. Bismuth--not apparently changed. Silver--deep gold, blue. Bismuth--yellow, blue. Silver--blue, yellow. Bismuth--dull colorless film.
Bismuth is slowly attacked with chlorine gas, much in the same way as with iodine and bromine in vapor.
At the common temperature neither bromine nor chlorine forms colored films upon this metal, which it is very difficult besides to bring to any high state of polish on account of its softness. But when lead is heated, as over the flame of a spirit-lamp, the vapors of bromine then form very fine colored films, which are in succession gold, deep blue, &c.
These two may be made to form colored films when combined rapidly together, but generally a dull coating without any spectral color is obtained, on account of the deliquescence of that salt.
Until we know the index of refraction of the different films enumerated, it would be impossible to give a correct table of the combining powers in the experiments that have been detailed; nor is the table of the relative thickness of transparent plates as it has been transmitted to us by Newton, sufficient in the present instance, if any great degree of precision be required. Besides these objections, it is necessary before leaving this subject to pass in review several others inseparable from the mode of performing the experiments themselves. The principal circumstances complicating these experiments and liable to vary in different observations, are,--