SflfHr' 
ATTRACTION. 
sid, tiiat every substance has more or less af- 
finity for all others, though it is certainly as- 
suming more than even analogy can war- 
rant, and is a point which we have no means 
of ascertaining. 
Affinity, like sensible attraction, varies 
with the mass and the distance of the attract- 
ing bodies. That cohesion varies with the mass 
cannot indeed be ascertained, because we 
have no means of varying the mass without 
at the same time altering the distance. But 
in cases of the adhesion of the surfaces of 
homogeneous bodies, which is undoubtedly 
an instance of homogeneous affinity, it 
has been demonstrated that the force of 
adhesion increases with the surface, which 
in some respect is the same as with the 
mass. 
That heterogeneous affinity increases 
with the mass has been observed long ago 
in particular instances, and has been lately 
demonstrated by Berthollet to take place 
in every case. Thus a given portion of wa- 
ter is retained more obstinately by a large 
rjuantity of sulphuric acid, than by a small 
quantity. Oxygen is more easily abstract- 
ed from oxides which are oxydised to a 
maximum, than front those which are oxy ded 
to a minimum. Lime only takes off the 
greatest part of the carbonic acid from 
potash, which still retains a portion of it ; 
and sulphuric acid does uot totally displace 
phosphoric acid from the lime united to it 
in phosphate of lime, a part of it remains 
undisturbed. In these and many other 
cases, a small portion of one substance is re- 
tained by a given quantity of another more 
strongly than a large portion ; and Ber- 
thollet has shewn, that in all eases a large 
quantity of one substance is capable of ab- 
stracting a portion of another from a small 
portion of a third, how weak soever the affi- 
nity between the first and second is, and 
how strong soever that between the second 
and third. 
That the force of affinity increases as the 
distance diminishes, and the contrary, is ob- 
vious ; for it becomes insensible, whenever 
the distance is sensible, and, on the other 
hand, it becomes exceedingly great, when 
the distance is exceedingly diminished. But 
the particular rate which this variation fol- 
lows is still unknown ; some have supposed 
the rate to be the same as that of sensible 
attraction, and that its intensity varies in- 
versely, as the square of the distance ; no 
sufficient argument has ever been advanced, 
to prove this law to be incompatible with 
the phenomena of affinity; but, on the 
VOL. I. 
other hand, no proof Las ever appeared in 
support of this opinion. 
Affinity agrees with sensible attraction in 
every determinable point : like sensible at- 
traction, it increases with the mass, and di- 
minishes as the distance augments ; conse- 
quently it is just to conclude, that attraction, 
whether it be sensible or insensible, is in ah 
cases, the same kind of force, and regulated 
precisely by tlie same general laws. 
The forces of affinity, though the same 
in kind, and possessing the same rate of va- 
riation with regard to distances, and also in 
respect to the mass, are vastly more nume- 
rous than those of sensible attraction ; for, 
instead of three, they amount to as many as 
there are heterogeneous bodies. But even 
when the distance and the mass are the 
same, as far as can be judged, the affinity 
of two bodies for a third is not the same. 
Thus barytes has a stronger affinity for sul- 
phuric acid than potash has ; for, on equal 
portions of them being mixed with a small 
quantity of the acid, the barytes seizes a 
much larger proportion of the acid than the 
potash does. The difference of intensity 
extends to all substances, for there are 
scarcely any two bodies whose particles 
have precisely the same affinity for a third, 
and scarcely any two bodies whose compo- 
nent parts adhere together with exactly the 
same force. , 
Because these affinities do not vary in 
common circumstances, like magnetism and 
electricity, but are always the same when 
other circumstances are equal, it has been 
argued that they do not, like them, depend 
on peculiar fluids, the quantity of which 
may vary ; but that they are permanent 
forces, inherent in every part of the attract- 
ing bodies. 
But after the extraordinary discoveries 
that have been lately made of the powerful 
effects which electricity, as excited by the 
galvanic apparatus, has in chemical attrac- 
tions : and when tiie great force of the affi- 
nity of the bases of potash and of soda to 
oxygen have been overcome by it, we must 
hesitate at least in continuing the above 
opinion; if we do not totally reject it, to 
adopt its reverse, and consider electric fire 
in future as the great agent of elective affi- 
nities. There is no reason why electric fire 
may not be subject to the same laws of at- 
traction as other substances, and why it may 
not remain united to bodies in a latent or 
inactive state, as well as caloric; we have 
already shewn, that the mass of any sub- 
stance has a powerful effect on its degree 
Ff 
