CHEMISTRY. 
nary principles, &c. In this manner sul- 
phur, by combining with oxygen and 
water, will form sulphuric acid, and this 
acid may be combined with a metal, so as 
to form a salt capable of giving out its 
acid again by heat. Our systematic books 
are written according to the supposition 
of secondary and more complicated prin- 
ciples; but the facts do not indispiifably 
prove their existence. 
When two bodies in the solid state which 
are disposed to combine are brought into 
contact, the combination will begin at 
the place where they touch, and if the 
compound be of such a nature, as that its 
freezing point (see Caloric) is lower 
than the common temperature of the bo- 
dies, it will be fluid, and the combination 
may proceed to the other parts of each 
till the whole shall have united. Thus 
snow and salt will form a fluid brine, if 
the temperature be higher than 6° below 
the commencement of Fahrenheit’s scale. 
If a solid be united with and suspended 
in a fluid, the former is said to be dissolved 
or in solution, and the fluid is called a 
solvent. In this manner water dissolves 
sugar or salt. Fluids in genera! dissolve 
greater quantities the higher the tempera- 
ttire, probably from tiie fluid state being 
promoted by heat. 
Some substances unite in all propor- 
tions, such as most acids in water ; but 
others have a limit ; as for example, water 
will dissolve only one fourth of its weight 
of common salt. It is then said to be 
saturated. But chemists use the word sa- 
turation in another sense. When two prin- 
ciples, as for instance, an acid and an alkali, 
are combined, the properties of each dis- 
appear when a due proportion of each is 
present; but if either of the principles 
exceed that proportion, the predominating 
property will be that of the principle 
which is in excess. In these cases the 
principles are said to be saturated when 
the properties are most completely ba- 
lanced ; but in the other cases the princi- 
ple which is defective in quantity is said 
to be super-saturated, or over saturated, 
and the other principle which is in excess 
is said to be under saturated : acids united 
with alkalies manifest these cases very strik- 
ingly. 
In the consideration of the phenomena 
of chemical or elective attraction between 
the principles of bodies, it will be very 
difficult to select instances for illustration, 
which shall be simple either as to the prin- 
ciples or the effects, because in almost 
every case there is a degree of complexity 
which obtains in nature, and even where 
wc suppose a great simplicity of principles, 
they may hereafter be discovered to be 
compound. But the doctrine will be un- 
derstood, and fixed in the memory by the 
examples to be brought ; in the same manner 
as when diagrams are used by geometri- 
cians, though the actual figures cannot strict- 
ly agree with their hypotheses or postulates'. 
1. The mutual action of two bodies ex- 
hibits the phenomena of simple elective at- 
traction and rejection : when two piinci- 
ples are presented to each other, they may 
either combine or reject each other. Thus 
water combines with and dissolves gum, 
but rejects camphor; and alcohol conr- 
bines with and dissolves camphor, but re- 
jects gum. 
It is probable that all simple bodies, 
if insulated, would combine together, and 
that the phenomenon of rejection, when 
it takes place, is an effect of some of the 
compound elective attractions, upon which 
we shall presently speak. 
When a body is suspended to saturation 
in a solvent, no more can be taken up or 
supported, becajise the cohesive attraction, 
or that of the parts of tlie body to each 
other, is stronger than that of the fluid 
to the same, and it is found that the 
power of the solvent is greater the less it is 
charged, until it ceases at the point of sa- 
turation. Elasticity, or the energy by 
which bodies are converted into gas or 
vapour, is likewise an opponent to solution 
6r combination, and gives a point of satu- 
ration which may be varied by preventing 
or impeding the assumption of the elastic 
state. 
2. When three bodies or principles are 
presented to each other in succession, 
we may conceive a variety of results, all 
which appear to take place in nature. 
Thus (a) they may not perceptibly unite, 
or (6) two may unite, and the third have no 
action either upon them singly or when in 
their combination; or (c) all three may 
unite from attractions exerted between 
each singly upon the others, and form a 
triple compound ; or (d) two of them may 
have no attraction for each other, but being 
both capable of combining with a third, 
this last may be the instrument of union 
between the two, and a triple compoimd 
will be thus formed. In this case the effect 
is said to be performed by intermediate 
attraction, and the attracting body is called 
