362 J. W. Langley—Chemical Affinity. 
supplements, out of a total of 9,665 pages only 62 are devoted 
to affinity where it appears under the head of Chemical Action. 
In Wurtz’s Dictionnaire de Chimie the treatment of affinity under 
the several heads of Chaleur, Electro Chimie, Affinité, Atomicité, 
ete., is relatively fuller, but still the proportion is quite small ; 
and in that excellent manual, Remsen’s Theoretical Chemistry, 
I. Tur Conception oF AFFINITY. 
The earliest appearance of the idea, which has since been 
named chemical affinity, is found in the writings of Hippocrates 
in the fifth century B. C., where the opinion is expressed that 
when two bodies unite to form a compound, a certain common 
principle must indwell in them, for it is laid down as a funda- 
mental postulate that “Like unites only with like,” hence the 
two bodies must possess some common principle, or have & 
bond of kinship between them.’ This conception prevailed 
with more or less clearness for several centuries, but it 1s not till 
the year 1698 that we find the word Affinitas employed and de- 
fined. It first occurs in the writings of the alchemist Barchusen," 
and the conceptions of Hippocrates were still the ruling ones. 
Thus Barchusen explains the impossibility of completely isolat- 
ing the four elements by saying that they have for each other a 
strong affinity which causes one to mingle with another, and 
which cause is derived from a principle common to them all. — 
Boerhaave, the celebrated physician of Leyden, in his 
elements of chemistry which appeared about 1782, was the first 
to extend the meaning of the term Affnitas or Verwandtschajt, 
since he says, “the effort also of like substances to unite is due 
to the working of the same force ;”* and elsewhere, in explain- 
aqua regia collect together in the bottom of the vessel. 
you not see clearly that there is between each particle of gold. 
