CHEMICAL AFFINITY. 137 



neous. By heterogeneous particles arc meant those which com. 

 pose different bodies ; thus a particle of iron, and a particle of 

 lead, are heterogeneous. 



Homogeneous affinity urges the homogeneous particles towards 

 each other, and keeps them at insensible distances from each 

 other; and consequently is the cau<=e why bodies almost always 

 exist united together, so as to constitute masses of sensible magni- 

 tude. This affinity is usually denoted by tlie term cohesion, and 

 sometimes by adhesion, when the surfaces of bodies are only 

 referred to. Homogeneous affinity is nearly universal ; as far at 

 is known, caloric and li^ht only are destitute of it. 



Heterogeneous affinity urges heterogeneous particles towards 

 each ott.er. and keeps them at insensible distances from each 

 other, and of course is the cause of the formation of new integrant 

 particles, composed of a certain number of heterogeneous par- 

 ticks. These new integrant particles afterwards unite by cohe- 

 sion, and form masses of compound bodies. Thus an integrant 

 particle of water r composed of particles of hydrogen and oxygen, 

 urged towards each other, and kept at an insrmible distance by 

 heterogenecus Affinity; and a mass of water is composed of an 

 indefinite number of integrant particles of that flu-d, urged to, 

 wards each other by homogeneous j ffi ity. Heterogeneous affinity 

 is un-ersal. as far as is known : that is to -ay. there is no body 

 whose particlf s art* not attracted by the particles of some other 

 body ; but whether the particles of all bodies hare an affinity for 

 the particles of all other bodies, is a point which we have no 

 means of ascertaining. It is, however, exceedingly probable, and 

 has been generally taken for granted ; though it is certainly assum- 

 ing more than oven analogy can warrant. 



11. Affinity, like sensible attraction, varies with the mass and 

 the distance of the attracting bodies. That cohesion varies with 

 the mass, cannot indeed be ascertained ; because we have no 

 method of varying the mass, without at the same time altering the 

 distance. Hut in cases of the adhesion of the surfaces of homo, 

 geneous bodies, which is undoubtedly an instance of homogeneous 

 affinity, it ha* been demonstrated, that the force of adhesion in. 

 creases with the surface, that is to say, with the mass ; for the 

 cumber of adhering particles must increase with the surface. 



That heterogeneous affinity increases with the mass, has been 

 observed long ago in particular instances, and has been lately 



