of elective Attractions. 153 
as the results which they indicate would follow from the com- 
parison of any other numbers, intermediate to the nearest of 
those, which are more correctly determined. I have not been 
able to obtain a sufficient number of facts relating to the me- 
tallic salts, to enable me to comprehend many of them in the 
tables. 
It has been usual to distinguish the attractions, which pro- 
duce the double decompositions of salts, into necessary and 
superfluous attractions ; but the distinction is neither very ac- 
curate, nor very important: they might be still further divided, 
accordingly as two, three, or the whole of the four ingre- 
dients concerned are capable of simply decomposing the salt 
in which they are not contained ; and if two, accordingly as 
they are previously united or separate ; such divisions would 
however merely tend to divert the attention from the natural 
operation of the joint forces concerned. 
It appears to be not improbable, that the attractive force of 
any two substances might, in many cases, be expressed by the 
quotient of two numbers appropriate to the substances, or 
rather by the excess of that quotient above unity ; thus the 
attractive force of many of the acids for the three principal 
alkalies might probably be correctly represented in this man- 
ner ; and where the order of attractions is different, perhaps 
the addition of a second, or of a second and third quotient, 
derived from a different series of numbers, would afford an 
-accurate determination of the relative force of attraction, which 
would always be the weaker, as the two substances concerned 
stood nearer to each other in these orders of numbers; so that, 
by affixing, to each simple substance, two, three, or at most 
MDCCCIX. X 
