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made upon the contents of separate beakers, and in each 
case on the day the lead foil was removed from the water, 
so that they were not all made on the same occasion. I felt 
it desirable to execute a fresh series of experiments in order 
to prove the accuracy, or otherwise, of the concliusion with 
regard to the amount of lead in solution diminishing on the 
foil and water being exposed for a lengthened period. 
Beakers were prepared with water and lead-foil (sea- water 
of course) and exposed ; but instead of determing the quan- 
tity of lead in solution, the lead-foil was removed after the 
same lapse of time as in the former experiments just de- 
scribed, namely, after 4, 7, 14, and 32 days’ exposure respec- 
tively, but the water from each exposure was kept and the 
whole of the water samples tested with ammonium sulphide 
at the same time, and thus by comparing the several depths 
of colour produced by the various samples comparative 
results were obtained; these confirming the former ones and 
supporting the conclusion that the amount of lead in solu- 
tion in the water diminishes on prolonged exposure along 
with the metallic surface. The same fact may be applied 
in the case of copper, as will be presently shown. 
The action of sea-water upon lead is very slight, and by 
another experiment (by immersing in a fresh portion of sea- 
water a piece of lead-foil used in the former experiments, 
which had become tarnished, and testing the water after 
some days’ exposure) it appears that no perceptible action 
is exerted by sea- water upon such tarnished metal. 
II. Copper . — The experiments about to be described were 
conducted similarly to those on lead, and, therefore, upon that 
point I need not dwell. By the action of the sea- water upon 
the copper a green deposit insoluble in water (or nearly so), 
but exceedingly soluble in dilute acids was formed, and this 
contained, as will be presently shown, the chief portion of 
the copper dissolved. This deposit was somewhat rapidly 
formed at the commencement of the exposure (some being 
