8 
dissolved as compared with those quantities found when 
the action was allowed to proceed in closed flasks ; never- 
theless, in every case — with one exception — considerably 
smaller quantities were dissolved when air was passed 
through the liquids, than when large surfaces of liquid were 
merely exposed to the action of the superincumbent air. 
I have already pointed out, when considering the influence 
of the extent of surface of lead exposed, that the only 
experiments in which a constant increase in lead dissolved 
(independent of the salt in solution, the time, &c.) was 
noticed, were those in which the lead was partially suspended 
in the liquids and partially surrounded by air, the liquids 
being contained in beakers and exposing a surface of about 
100 sq. cm. to the surrounding air. If we compare the 
quantities of lead dissolved under these conditions with the 
quantities dissolved in experiments carried out in a precisely 
similar manner, except that the lead was wholly surrounded 
by liquid, we find that there was a small but constant 
increase in the former cases; the quantities dissolved in 
these cases were not so large as those which passed into 
solution when the experiments were carried out in basins 
and the lead was wholly immersed in the liquid. On the 
whole then the exposure of the various liquids to a large 
surface of air appears to cause an increase in the quantity of 
lead dissolved : this increase becomes specially marked after 
the lapse of considerable periods of time. 
7. Do the solvent actions of dilute saline solutions upon 
lead continue during lengthened periods of time, or is there 
a limit reached after which little or no further action is ex- 
ercised upon the lead ? 
By consulting the two tables it becomes very evident 
that so far as these experiments allow one to judge there is 
a constant increase of lead dissolved with increase of time 
of action, except in the case of those solutions which con- 
tain carbonate of potassium, This increase appears to be 
