Henry's Chemistry. 335 



bodies composing the material system of the universe, have a mu- 

 tual tendency to approach each other, whatsoever may be the 

 distances at which they are placed." Newton established, on the 

 contrary, that when these distances are diminished to a certain 

 point, the attractive forces cease to operate, and the repulsive 

 begin to act. This subject has been amply investigated by 

 Boscovich. 



In the following sentence, Dr. Henry's language is contrary to 

 the usage of all good chemical authors. " By the affinity of aggre- 

 gation, the cohesive affinity, or more simply cohesion, is to be un- 

 derstood that force or power, by which particles or atoms of matter 

 of the same kind, attract each other, the only effect of this affinity 

 being an aggregate or mass." The term affinity thus employed, 

 tends to introduce confusion into chemical discussions. GeofFroy 

 originally used it to designate those relationships between two or 

 more sets of heterogeneous particles, which caused them to unite 

 into a compound whole ; and every chemical writer since, has we 

 helieve, used affiniti/ as synonymous with the attraction of com- 

 position, in contradistinction to the attraction of aggregation or 

 cohesive attraction. In fact, the expression cohesive affinity is a 

 solecism, for a thing cannot be said to have an affinity or relation- 

 ship to itself. We might as well say of a person, that he is related 

 to himself. Precision of language is a primary virtue in an ele- 

 mentary writer. 



In the same paragraph, Dr. Henry goes on to say, " But in com- 

 pound bodies, we may distinguish the force with which the pri- 

 mary or component atoms are united, from that which the compound 

 atoms exert towards each other ; the former being united by che- 

 mical affinity, and the latter by the cohesive attraction." This is 

 a ?we;«physical distinction, which he might as well have let alone, 

 for probability is against it. In considering for example an atom 

 of calcareous spar, we may contemplate its solidity as resulting 

 from the attractive affinity of an atom of carbonic acid for an atom 

 of lime; or of one atom of calcium, one of carbon, and three of 

 oxygen. Let a second atom of calcareous spar be brought into 

 intimate association with the first. The aggregate may be held 

 together either by the reciprocal affinities of the two ultimate atoms 

 of calcium, two of carbon, and six of oxygen, or by those of the 

 two atoms lime and carbonic acid, or by the cohesion of an atom 

 ofcarbonatc of lime to carbonate of lime. We cannot help recog- 

 nising the co-operation at least, of the former set of forces in the 

 formation of the aggregate ; for arrange the ultimate atoms in the 

 solid as we please, still one of carbonic acid will be situated 

 between several of lime, and will exert a greater or less affinity 

 for them all, relative to its position and proximity, and be acted 

 on by several atoms of lime in return. 



The first section of the Chapter on Chemical Affinity treats of 



