Inquiry into the Causes of Light and Colour. 
199 
deprived of oxygen and combined with phlogiston, and in this manner would I ac- 
count for their solution in acids. Acids are said to dissolve metals by oxydating them ; 
this process would, I suspect, obstruct and prevent their solution. I have attempted 
to show that their operation on colouring matter is directly the reverse, and I very 
strongly suspect that the same is the case with regard to metals. Acids are in com- 
mon use in the arts for cleansing metals and rendering them perfectly pure ; tartar, 
alum, and common salt, mixed in certain proportions, have even the property of 
whitening brass and copper ; gold and platina are dissolved by chlorine, and when 
dissolved by n it ro -muriatic acid the same compounds are the results as when chlo- 
rine alone is the solvent. 
All metals are held more permanently in solution by chlorine and muriatic acid 
than by other acids. Present to acids metals combined with much oxygen, the acids 
cannot dissolve them; perhaps the oxyde takes oxygen from the acid, and acids can- 
not dissolve oxydes. I consider all these circumstances as tending to show that the 
action of acids on metals is disoxygenating. I conceive that carbonic acid gas de- 
stroys life and combustion by taking oxygen from the animal and burning body. 
Should this be so, that acids disoxygenate metals in order to dissolve them, then the un- 
named principle would attract the oxygen and phlogiston, and the base with which 
it should be united attract the metallic base. Phlogiston may be given out by either 
the unnamed principle, or the metal, or both ; and thus, when saturation has taken place, 
the oxygen, for want of the necessary quantity of phlogiston to form a metal by 
combining with the metallic base, precipitates with it in the form of an oxyde. If, on 
the contrary, metals or combustible substances precipitate the metallic base, they 
supply the necessary portion of phlogiston, and the metal is regenerated in its me- 
tallic state. 
Should what I have advanced on chemical phenomena render generally probable 
the existence of this principle, then combustion may be the combination of the com- 
bustible with oxygen, and the union of the unnamed principle with phlogiston ; the 
latter, under cei tain circumstances, constituting light. There is nogreater difficulty to 
be overcome for maintaining this supposition than for explaining chemical facts in 
general. To constitute any body a number of conditions arc always absolutely neces- 
sary ; so many atoms of such an alkali and such an acid may be the constituents of 
such a salt, and yet it is evident that they may be dissolved together in the same 
menstruum without the salt being formed. In like manner so much phlogiston and 
so much of the unnamed principle may be necessary to produce light, and yet we can 
suppose them to be present under circumstances where light may not he the conse- 
quence. If light be the effect of phlogiston and the principle supposed, chemically 
combined in certain proportions, the proportions and the combination are indispen- 
sable requisites. Is it not conceivable that the proportions and combination maybe 
so exact and perfect and so independent of external circumstance, that no sensible 
heat should be given out? And on this supposition may not the comparative perma- 
nency and low temperature of phosphorescent objects be accounted for ? Or inay not 
the proportions and combination be in such a state, or so counteracted by other 
bodies, as to give out great heat without produciog light? or under another set of cir- 
cumstances give out both heat and light? Besides which, the eye must be an exceed- 
ingly uncertain test of the quantity and presence of light under a vast variety of cir- 
cumstances. Light then may possibly be phlogiston aud the supposed principle in 
a state of chemical combination: this principle would probably occupy the upper 
regions of the atmosphere, thus presenting itself to the phlogiston in the purest and 
most proper state for chemical union. And phlogiston transmitted by reflection would 
be likely to be diminished in quantity, and therefore to produce a paler, or in other 
words less light, and which would be attended therefore with but little redundant 
heat or uncombined phlogiston. Then what is colour ? perhaps it might be consider- 
ed as the decomposition and consequent diminution of light. I have observed that 
oxygen and phlogiston appear to be* antagonist principles, and that commonly as 
one is combined w ith any body the other is set free. 1 conceive that colour may be 
occasioned by white light exchanging a portion of phlogiston for a portion of oxygen, 
by which the density of the particles is increased, which determines the nature and 
shade of the colour, that the intensity of light is diminished, and when saturation 
has taken place, is extinguished, and black is the consequence. 
Should these opinions be W’ell founded, then colour is a decomposition of the 
coloured substance ; the light by greater affinity appropriating the oxygen, and the 
coloured substance taking the phlogiston. In this way may be explained the fading 
Hence perhaps polat ity, electricity, #c. 
