Modifying the force of Chemical Attraction. 241 
to follow in the track of observation and experiment, it ap- 
ears to me that we must admit it to be a law of extensive 
Jfinity: and having admitted it, apply it in the explanation 
he principal obstacle to the general reception of these 
views, seems to have been found in their supposed inconsist- 
tion,) that there are in the boiling liquid, four different sub- 
stances, sulphate of baryta, sulphate of potassa, baryta and 
potassa ; the influence of the uncombined baryta, being ex- 
erted to prevent the decomposition of the sulphate of baryta 
from proceding any farther, and that of the uncombined a 
tassa to maintain in existence the sulphate of potassa that 
has been already formed. 
I will, in closing, only call the attention of any reader of 
the Journal, who may have had the patience to accompany 
me thus far, to the following extract from the preface to 
Thomson’s First Principles of Chemistry. — 
“ But it is much more difficult to obtain substances ina 
state of complete purity, than chemists in general are aware ; 
Vor. XVI.—No. 2. 4 
