ATTRACTION. 



is a point which we have no means of as- 

 certaining 1 . 



Affinity, like sensible attraction, varies 

 with the mass and the distance of the at- 

 tracting- 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 ho- 

 mogeneous affinity, it has been demonstra- 

 ted, that the fbrce 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 por- 

 tion of water is retained more obstinately 

 by a large quantity of sulphuric acid, than 

 by a small quantity. Oxygen is more ea- 

 sily abstracted from oxides which are ox- 

 ydised to a maximum, than from those 

 which are oxyded to a minimum. Lime 

 only takes off' the greatest part of the car- 

 bonic acid from potash, which still retains 

 a portion of it ; and sulphuric acid does 

 not 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 por- 

 tion of one substance is retained by a given 

 quantity of another more strongly than a 

 large portion ; and Berthollet has shewn, 

 that in all cases a large quantity of one 

 substance is capable of abstracting a por- 

 tion of another from a small portion of a 

 third, how weak soever the affinity be- 

 tween 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 obvious; 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 follows is still unknown ; 

 some have supposed the rate to be the 

 same as that of sensible attraction, and 

 that its intensity varies inversely, as the 

 square of the distance ; no sufficent ar- 

 gument has ever been advanced, to prove 

 this law to be incompatible with the phe- 

 nomena of affinity; but, on the other 

 hand, no proof has ever appeared in sup- 

 port of this opinion. 



Affinity agrees with sensible attraction 

 irt every determinable point : like sensible 



attraction, it increases with the mass, and 

 diminishes as the distance augments ; 

 consequently, it is just to conclude, that 

 attraction, whether it be sensible or in- 

 sensible, is, in all cases, the same kind of 

 force, and regulated precisely by the 

 same general 'aws. 



The forces of affinity, though the same 

 in kind, and possessing the same rate of 

 variation with regard to distances, and 

 also in respect to the mass, are vastly 

 more numerous than those of sensible at- 

 traction ; 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 the 

 third is not the same. Thus barytes has 

 a stronger affinity for sulphuric 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 ex- 

 tends 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 

 component 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 attracting bodies. 



But after the extraordinary discoveries 

 that have been lately made of the power- 

 ful effects which electricity, as excited by 

 the galvanic apparatus, has in chemical 

 attractions, and when the great force of 

 the affinity of the bases of potash and of 

 soda to oxygen have been overcome by it, 

 we must hesitate at least in continuing 1 

 the above opinion, if we do not totally 

 reject it, to adopt its reverse, and consi- 

 der electric fire, in future, as the great 

 agent of elective affinities. There is no 

 reason why electric fire may not be sub- 

 ject to the same laws of attraction 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 substance 

 has a powerful effect on its degree of 

 affinity; many of the effects of electric 

 fire on affinity might be explained by this 

 increased power of it, when acting 1 in a 

 mass, or, at farthest, by supposing 1 that its 



