148 
treatment to which it has been subjected, which influences 
the solvent action of dilute saline solutions upon that lead. 
But the most remarkable feature in the numbers contained 
in Table VI. is the extraordinary falling off in the quantities 
of lead dissolved from No. 2 commercial sample when the 
experiments were carried out in beakers, as compared with 
the quantities dissolved in corked flasks. Taking, for in- 
stance, a solution of Ammonium Nitrate containing 0-20 
grams, of the salt per litre of water, it is found that 500 
cbc. of this liquid, acting upon a surface of 25sq. cm. of 
lead, dissolves 12-0 mgms. after 6 days’ action, when the ex- 
periment is carried out in a corked flask nearly filled with 
liquid; but that the same quantity of the same solution 
acting on the same surface of the same lead is only able to 
bring a slight trace (i.e. less than 0.20 mgm.) of lead into 
solution, after the expiry of the same time, when the experi- 
ment is conducted in a beaker half filled with liquid and loosely 
covered with porous paper. The conclusion appears to be 
that the action of the air results in the formation of an in- 
soluble lead salt. That this conclusion is the correct one 
appears from the following experiments. In the experiments 
with No. 2 sample of commercial lead very considerable 
precipitates formed on the lead itself and on the bottom of 
the vessels used. This was the case both in those experi- 
ments which were carried out in corked flasks and in those 
in beakers, but in the latter cases the precipitate generally 
appeared somewhat more bulky. On withdrawing a quantity 
of the clear liquid — ^holding lead in solution — from the flasks, 
and exposing it to the action of the air, a precipitate was in 
each case almost immediately formed. This precipitate 
increased in amount, until after a few hours a mere trace of 
lead could be detected in solution : the whole of the lead 
had been precipitated in an insoluble form. The corks were 
then withdrawn from the flasks, and the mouths loosely 
