CHR 
coverics of Sir Isaac Newton, however, 
are sufficient to justify the following apho- 
risms. 
1. All the colours in nature arise from the 
rays of light. 2. There are seven primary 
colours ; namely, red, orange, yellow, green, 
blue, indigo, and violet. 3. Every ray of 
light may be separated into these seven pri- 
mary colours. 4. The rays of light, in pass- 
ing through the same medium, have differ- 
ent degrees of refrangibility. 5. fhe differ- 
ence in the colours of light arises from its 
difi'erent refrangibility ; that which is the 
least refrangible producing red; and that 
which is the most refrangible violet. 6. By 
compounding any two of the primary, as 
red and yellow, or yellow and blue, the in- 
termediate colour, orange or green, may be 
produced. 7. The colours of bodies arise 
from their dispositions to reflect one sort of 
rays and to absorb the others ; those that 
reflect the least refrangible rays appearing 
red, and those that reflect the most refran- 
gible violet. 8. Such bodies as reflect two 
or more sorts of rays, appear of various 
colours. 9. The whiteness of bodies arises 
from their disposition to reflect all the rays 
of light promiscuously. 10. The blackness 
of bodies proceeds from their incapacity to 
reflect any of the rays of light. And from 
their thus absorbing all the rays of light 
that are tlirown upon them, it arises, that 
black bodies, when exposed to the sun, be- 
come hot sooner than all others. 
Sir Isaac Newton, in the course of his in- 
vestigations of the properties of light, disco- 
vered that the lengths of the spaces occu- 
pied in the spectrum by the seven primary 
colours exactly correspond to the lengths 
of chords that sound the seven notes in the 
diatonic scale of music; which is made evi- 
dent by an experiment. On a paper, or 
other fit substance, in a darkened room, let 
a ray of light be refiacted by means of a 
prism into a spectrum of some size, mark- 
ing upon it tire precise boundaries of the 
several colours : and it will be found that 
the spaces by which the sever al colours are 
bounded, viz. the space containing the red, 
that containing the orange, yellow, &c. will 
be in exact proportiosr to the divisions ot a 
musical chord for the notes of an oirtave ; 
that is, as tire intervals of these ; 1 ; | | | ; 
I; I’’ -Ri 2- CoLOL'KS, Optics, &c. 
CHROME, a metal discovered by Vau- 
quelin. It exists in the state of an acid, 
combined with oxide of lead, in a beautiful 
mineral named red lead, found in Siberia, 
and with regard to which very discordant 
CHR 
analyses had been given by different clre- 
inists. Vauqiielin reduced the metallic acid 
which he discovered in it to the metallic 
state, and his researches have been confirm- 
ed by those of Klaproth and Gttrelin. It 
derives its name from the splendid and nu- 
merous colours which it presents in its saline 
combinations. It has since been discover- 
ed in various minerals. The rrative chro- 
mate of lead, or the red lead of Siberia, is 
generally crystallized in oblique tetrahedral 
prisms. Its colour is a fine aurora red ; its 
lustre shilling, and intermediate between 
adamantine and resinous ; the crystals are 
transliicid ; the fracture is uneven ; the 
specific gravity 6.0269. It decrepitates 
before the blow-pipe, and melts into a 
blackish scoria. It colours borax green by 
fusion. According to Vaiiquelin, it is com- 
posed of 57.10 of lead, 6.86 of oxygen, and 
36.04 of chromic acid. There is found 
with the chromate of lead, a mineral of a 
green colour in minute crystals, which Vau- 
quelin found to be composed of the oxides 
of chrome and lead, and which, as he con- 
jectures, has probably originated in tlie de- 
composition of the perfect chromate, from 
some process by which part of its oxygen 
has been abstracted. 
Native chromate of iron has mhre lately 
been found in the department of Var in 
France, and likewise in Siberia. This mi- 
mineral is massive, of a blackish brown co- 
lour, with no great lustre and opaque ; its 
fracture is uneven, and it is hard and diffi- 
cult to break ; its specific gravity is 4.0. It 
is scarcely fusible before the blow-pipe, but 
with borax it melts into a glass of a fine 
green colour. According to an accurate 
analysis of it, it consists of 63.6 of chromic 
acid, or perhaps rather oxide of chrome, 
and 36 of oxide of iron. 
Chrome has been also found in smaller 
quantities in other minerals, paj ticularly in 
some gems, of which it appears to be the 
colouring principle. It exists in the eme- 
rald, in the state of green oxide, and in 
the spinal ruby, in the state of acid. 
Vauquelin extracted the metal from the 
red lead ore, by adding to it muriatic acid, 
which combines with the oxide of lead, and 
forms a compound that is precipitated, the 
chromic acid remaining in solution- To ab- 
stract a little muriatic acid combined with 
it, oxide of silver is cautiously added,' and 
the pure chromic acid being decanted from 
the precipitate of muriate of silver, and eva- 
porated, is exposed to a very strong heat 
excited by a forge, in a crucible of char- 
