, 
, 
ed it may be preserved 
- a long time in presence of a solution of chlorid of calcium. _ 
94 Correspondence of J. Nickles. 
that the whole had the effect of a bronze, while at the beginning 
of the experiment before the eye had become fatigued, it was eas 
to distinguish between the violet of the chlorophyl and the livid 
green of the flesh color. 
Employment of the Sodium flame by artists——We have previ- 
ously shown that the different colors of the spectrum may be 
reduced to white or black, unless they contain blue which is the 
only color unaffected by the soda flame. 
In observing such a spectral image it will be noticed, that if 
all the colors are reduced to either white or black, the borders 
are more or less darkened or dulled as in a photograph of the 
spectrum. Looking at a painting, especially a pastel containing 
very little if any blue, under these conditions, one is struck with 
the fact, that although the colors vanish, the grayish tone which 
represents them gives the appearance of a pencil drawing. The 
model or plan exists by reason of the half tints so that by the 
monochromatic light, one is sometimes able to go back to the de- 
sign without touching the picture and can thus give in some sort 
the pe a of a work of art. 
The flame of sodium may yet aid the painter in comparing 
shades, in grouping colors and weighing their tones 
e same manner, two colors, for example two greens which 
appear identical upon the palette, in the daytime, may be differ- 
ent when seen by common evening light, and are more likely to 
differ when viewed by the sodium flame, one being decolorized 
and the other transformed into black. In the same manner, 0 
two reds seen under the same conditions, one may appear white, 
while the other containing blue, will assume a 2olei-tint comple- 
mentary to the yellow of the monochromatic flame. 
Common salt ignited on a platinum wire in the flame of a 
Bunsen burner, strikingly exhibits the chemical differences which 
sometimes exist between two similar shades of color. This 
eebe rere 
It is prepared by passing a current of chlorine into chl 
