if a continued interference of omnipotent powei was constantly being ex 
sition, we sli3.ll perceive tli3t their term, their taste, and their consistence, 3 ie changed in combination, 
and we cannot est3bhsh any rule to indicate, a priori , ull the changes which may aiise, and the natuie 
and properties of the body which shall be formed. 
Law IV". Every individucil substance has its peculiar affinities with the various substances pi e- 
sented to it. 
If all bodies had the same degree of affinity with each other, no change could take place amongst 
them; we should not be able to displace any principle by presenting one body to anotheu Nature has 
therefore wisely varied the affinities, and appointed to each body its relation with all those that can be 
presented to it. 
It is in consequence of this difference in the affinities, that all chemical decompositions are effected: 
all the operations of nature and art are founded upon it. It is therefore of importance to be well 
acquainted with all the phenomena and circumstances which this law or decomposition can present 
to us. 
The affinity of composition has received different names, according to its effects; it is divided into 
simple affinity, double affinity, the affinity of an intermedium, reciprocal affinity, &c. 
]. Two principles united together, and separated by means of a third, afford an example of simple 
affinity; it consists in the ^displacing of one principle by the addition of a third. Bergman has given it 
the name of Elective Attraction. 
The body which is disengaged, or displaced, is known by the name of the Precipitate. An alkali 
precipitates metals from their solutions; the sulphuric acid precipitates the muriatic, the nitric, &c. 
The precipitate is not always formed by the disengaged substance. Sometimes the new compound 
itself is precipitated; as, for example, when I pour the sulphuric or vitriolic acid on a solution of mu¬ 
riate of lime. Sometimes the disengaged body and the new compound are precipitated together; as, 
for example, when the sulphate of magnesia or Epsom salt is dissolved in water, and precipitated by 
means of lime water. 
2. It often happens that the compound of two principles cannot be destroyed either by a third or 
a fourth body separately applied; but if these two bodies be united, and placed in contact with the 
same compound, a decomposition or change of principles will then take place. This phenomenon 
constitutes double affinity. An example will render this proposition more clear and precise. The 
sulphate of pot-ash or vitriolated tartar is not completely decomposed by the nitric acid or by lime, 
when either of these principles are separately presented; but, if the nitric acid be combined with lime, 
this nitrate of lime will decompose the sulphate of pot-ash. In this last case the affinity of the sul¬ 
phuric acid with the alkali is weakened by its affinity to the lime. This acid, therefore, is subject to 
two attractions; the one which retains it to the alkali, and the other which attracts it towards the 
lime: Mr. Kirwan has named the first the Quiescent affinity, and the other the Divellent Affinity. 
The same may be said respecting the affinities of the alkali; it is retained to the sulphuric acid by a 
superior force, but is nevertheless attracted by the nitric acid. Let us suppose, now, that the sulphuric 
acid adheres to the alkali with a force as 8, and to the lime by a force expressed by the number 6; that 
the nitric acid adheres to the lime by a force as 4 , and tends to unite with the alkali by a force as 7. It 
may then be perceived that the nitric acid and the lime, separately applied to the sulphate of pot-ash, 
would not pioduce any change: but if they be presented in a state of combination, then the sulphuric 
acid is attracted on the one hand by fi, and retained by 8; it has therefore an effective attraction to the 
alkali as 2. On the other hand, the nitric acid is attracted by a force as 7, and retained by a force as 4; 
it therefoie ietain.3 a tendency to unite with the alkali, which is denoted by the number 3 ; and conse¬ 
quently it ought to displace the sulphuric acid, which is retained only by a force as 2. 
3 . There are cases in which two bodies, having no perceptible affinity to each other, obtain a dis¬ 
position to unite by the intervention of a third; and this is called the affinity of an intermedium. An 
alkali is the intermedium of union between oil and water; hence the theory of lixiviums of washing 
&c. &c. * 
If the affinities of bodies were well know n, we might foretel the results of all operations: but it 
