370 - J. W. Langley—Chemical Affinity 
shadowed from speculations concerning the value of chemical 
attractions before Dalton’s hypothesis was given to the world. 
An English chemist, William Higgins, Professor of Chem- 
istry to the Dublin Society, published in 1789 a work in 
which the composition of several bodies is attributed to the 
” . 
up the sulphur compound nor the sulphur the iron compound, 
but both the phlogisticated iron and sulphur will be united into 
a compound system by this residual force of two existing 
between the groups. This is exactly what would be repre- 
sented by the equivalent symbol for ferrous sulphate, FeO, SO,, 
where the oxide of iron FeO, and the sulphuric acid SO,, were 
each regarded as entire or binary compounds united to form 
the ternary body, FeO, SO,. 
Shortly after these attempts of Higgins, we. find, in the open- 
ing years of the present century, three general methods indi- 
cated for the study of the force of affinity. Instead of being 
successively taken up and abandoned, like all preceding specu- 
lations, they have remained steadily in use during the eighty 
years which have intervened, and they are to-day still the most 
promising means at our disposal. These three methods may 
be called the thermal, the electrical and the method of time or 
speed. It will be convenient to consider each one separately. 
The thermal method was first indicated by Lavoisier 10 4 
moir, a portion of which will bear quotation. He says: 
m t any tem- 
perature below zero (Centigrade) an acid with ice, it (the acid) 
will melt it until it is so enfeebled that its attractive force 00 
the molecules of the ice becomes equal to the force which 
makes these molecules adhere to each other, and which 1s 80 
much the greater as the cold is more considerable; thus the 
degree of concentration at which the acid will cease to dissolve 
the ice will be so much the greater as the temperature of the 
mixture is lowered below zero, and we can refer to the degrees 
of the thermometer the affinities of acids for water according 10 
various degrees of concentration.” 
