198 
Inquiry into the Causes of Light and Colour. 
er consideration than it is in my power to bestow upon it ; I will, however, with a 
view of explaining the theory of light and colours, upon the assumption of the ex- 
istence in the atmosphere of another principle besides that which combines with bo- 
dies during combustion, venture to say a fewwordsuponthistopic. Chemical pheno- 
mena often seem to he at variance with any general rules; and although there can 
he little doubt that a general rule obtains, yet the change in the relation towards each 
other of subtle substances, the existence perhaps of fluids of which wc can obtain 
no satisfactory evidence, and their modifying influence upon which we cannot cal- 
culate, render argument imperfect and inconclusive, because it must necessarily be 
founded upon a very partial and clouded view of facts. 
Stahl explained combustion upon the assumption, that the burned body lost phlo- 
giston. Lavoisier overturned the hypothesis by demonstrating that by tindergoing 
combustion bodies did not lose, but gain; and he further showed, that their gain pro- 
ceeded from an accession of oxygen. I think Lavoisier took away from our know- 
ledge as much as he added to it, and that, instead of using his discovery to subvert 
and destroy the old doctrine, he should have added the one to the other, and blended 
them both together. I cannot prosecute the investigation of this subject further than 
may be necessary to the exposition of the theory of light and colour; so that my re- 
marks may only have the effect of rendering darkness visible; they may perhaps 
discover the nakedness of the land, but be little calculated to dress and improve it. 
Phlogiston is the life of chemistry ; without it, the science would be destitute of all 
truth and likelihood. Chemical action never takes place without effecting a change 
in the relation of substances towards each other; and the avidity of all bodies for 
phlogiston and oxygen occasions them to be the chief instruments in producing che- 
mical action by means perhaps, generally, of antagonist powers. The effect caused by 
alkalis and acids on colours could not escape observation, and consequently cer- 
tain colours were made the test of the presence and absence of these agents ; per- 
haps in their action upon oxygen aud phlogiston, acids may take away oxygen and 
communicate phlogiston, and thus promote solution ; whilst alkalis may abstract 
phlogiston and impart oxygen, and thus favour insolubility. But though this may be 
true in fhe instance cited, and in a great many more, yet certainly it is not univer- 
sally. So far from it that, wc frequently find a number of highly oxydated bodies ex- 
tremely soluble. Is it not possible that this may lrcowing to another principle? Where a 
combustible substance for instance is converted into charcoal, the phenomena observ- 
able (setting aside the consideration of the products) arc a change of colour, through 
all the grades of white, yellow, and brown, to black ; and a correspondent change in 
its solubility till it ends in being one of the most insoluble things in nature. Now 
these effects are perhaps the result of the loss of phlogiston and the union of oxy- 
gen with carbon ; more oxygen being the same as more colour and greater insolu- 
bility, and the converse. But should this charcoal be burnt with free access of air, 
what happens ? Why it is dissolved into a gas, and has no colour at all. Oxygen 
we have hitherto found to cause colour and insolubility, and to expel phlogiston: 
does it all at once change its nature, unite with phlogiston, destroy colour, and be- 
come eminently solvent? Should oxygen not be a compound body’, there might yet 
he another principle in the atmosphere, union with which may be the cause of its 
assuming the gaseous form, and producing effects seemingly soopposite; this prin- 
ciple may dissolve oxygen, and phlogiston mav dissolve carbon, and these consti- 
tuents may be in antagonist states to each other, their mutual necessities, like the 
wants of mankind, being the cause of their congregation. This idea of the compo- 
nent bodies of some fluids, and perhaps also solids, being in antagonist relation to 
each other, was forced upon me by what I observed with regard to colours. Indigo 
is insoluble ; certain substances capable of depriving it of oxygen destroy its colour 
and dissolve it. These substances and the indigo, although dissolved together in the 
same fluid, cannot possibly be in chemical union, being in a state of counteraction. 
Perhaps one substance barters its oxygen for the other’s phlogiston. Sulphur, oii 
this supposition, may be a base with oxygen, and its conversion into an acid analo- 
gous to what has been suggested respecting carbon. Metals may be bases with phlo- 
giston and bases with oxygen; hut being for the most part incapable of uniting with 
phlogiston per se in an antagonist relation to oxygen and the unnamed principle, 
and forming acids, they enter into a further union with oxygen and become oxydes*. 
But though incapable of this combination per se, yet I am disposed to think that, aided 
by the afhnity of other bases, such as nitrogen, sulphur, chlorine, &c. they may he 
* There is some obscurity here which it is impossible 
to the author. The MS, affords us no assistance. — Kn. 
to clear up by reference 
