PRODUCED BY BODIES ACTING BY CONTACT. 5 
of the soluble salts which surround them; but they may be 
finally removed by edulcoration. 
JT dissolved some nitrate of barytes in ten parts of water ; after 
having precipitated nearly the half of this by sulphuric acid, when 
the precipitate was settled, I determined the quantity of nitrate 
of barytes which the clear liquid above the precipitate contained. 
The filtrated liquid coming from the washing of the precipitate 
was evaporated, and the quantity of nitrate of barytes which it 
contained ascertained. By subtracting the weight of this nitrate 
and the weight of the sulphate of barytes obtained from the total 
weight of the moist precipitate, the weight of the water contained 
in the liquid was ascertained. Calculating according to these 
data, on the one hand the weight of the nitrate of barytes con- 
tained in the liquid supernatant upon the sulphate formed, and 
on the other hand that of the liquid which moistened the preci- 
pitate, we find that two-thirds only of this last were dissolved, 
and that the remaining one-third, which is found in the water 
employed for edulcoration, must be condensed by the attraction 
exercised by the precipitated sulphate. If, instead of precipi- 
tating a solution of nitrate of barytes, chloride of barium be 
employed, none of this latter is carried down. But if a solution 
of nitrate and of sulphate of soda be precipitated by the nitrate 
of barytes, and the precipitate be washed until a drop of the 
water no longer leaves any trace of solid matter upon evapora- 
tion on platina foil, the sulphate of barytes in this case is able to 
retain 2 per cent. of nitrate of soda; in order to remove which 
the precipitate must be calcined and afterwards washed. 
The sulphate of barytes thus exercises so feeble an attraction 
vn the chloride of barium, that it cannot abstract it from its 
aqueous solution; with respect to the nitrate, the attraction is 
already sufficiently strong to render a large quantity of water 
necessary to remove it; but the water is incapable of completely 
removing from the sulphate of barytes the nitrate of soda which 
it takes up when in the act of forming. 
_ We may very well estimate the force of attraction which solid 
bodies mutually exert on one another, by considering the action 
of strong glue on wood and glass; if a plate of glass be covered 
with a moist bladder, and after drying it we attempt to detach 
it, we remove morsels of glass. The attraction exercised by the 
bladder upon the glass is therefore stronger than the cohesion 
of the molecules of the glass itself; but if the plate of glass 
