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cleaned by immersing for a sufficient time in moderately 
dilute nitric acid, and afterwards washing in water. The 
lead was cleaned and made perfectly bright by rapidly 
rubbing with the back of a knife. The pieces were cleaned 
shortly before being immersed in the sea- water, and until 
ready for such immersion were kept covered by pure water. 
The quantities of sea-water (2,000 grain measures in each 
instance) were poured into beakers, and one of the pieces of foil, 
copper or lead as the case might be, was dropped into each. 
The beakers were then placed in a room above the laboratory, 
where they were covered by pieces of porous paper. The 
foil was occasionally moved about during the exposure. 
I. Lead . — Even after the longest exposure — 32 days — no 
insoluble compound was suspended in the water or precipi- 
tated to the bottom of the beaker, but the surface of the foil 
was slightly coated with a deposit ; it was tarnished. The 
standard solution of lead from which the comparison solutions 
were constructed was prepared by dissolving one grain of 
the lead foil in as small a quantity of nitric acid as possible 
and diluting with water to 2000 measures : each 100 mea- 
sures being then equal to 0'05 of a grain of lead. The fol- 
lowing results were obtained : — 
Days exposed. Lead in water. 
4 0-000862509 grains. 
7 0-00120750 
14 0-00138000 
32 (experiment 1) 0-00093875 „ 
32 (experiment 2) 0-00086250 „ 
These results show that from the 14th day of exposure to 
the 32nd the quantity of lead in solution diminished (ac- 
cording to experiment 2) from 0-00138 to 0-0008625 of a 
grain, a quantity exceedingly small, but sufficient to dis- 
tinctly show a diminution, and easily detected by the method 
adopted, in the quantity of water used — 2000 grains. 
I should explain that the determinations as above were 
