REMOVAL OF SILVER AND GOLD BY MUNTZ METAL. 365 
Next the scale from the ten old sheathings gave an average of 
Silver. Gold 
5 oz. 17 dwt. 8 gr. per ton. 8 dwt. 1°8 gr. per ton. 
or an average increase in round numbers of over 7 dwt. of gold, 
and an average decrease of 4 oz. 6 dwts. 23 grs. of silver as com- 
pared with the new muntz metal. 
The amount of gold yielded by the old metal and the scale is 
probably understated, since the chlorides could not be entirely 
removed from the old metal and they were very abundant in the 
scale, hence on dissolving in nitric acid some of the gold passed 
into solution as chloride and was lost. 
The results do not altogether agree with the previously pub- 
lished views nor with my own before I commenced the investiga- 
tion. The silver has not accumulated, but on the contrary 
decreased, the scale however, contains a larger amount of gold. 
The increase of gold in the scale may be due to the deposition of 
gold from the sea-water on to the surface of the metal, or it may 
_ be due to the comparative non-solubility of gold in sea-water; 
the muntz metal having been corroded and dissolved away, 
together with much of the silver leaving the gold behind ; it is 
probably due to both causes, 7.e., partly to deposition and partly 
to accumulation, for the superficial parts of the experimental 
plates Nos. 1; la and 7, obtained by scraping them, show an. 
increase in the amount of gold and a decrease in the amount 
of silver, the increase in the gold cannot in these cases, well be 
due to mere accumulation, since the plates do not appear to have 
lost sufficient weight to materially increase the proportion of the 
residual gold. 
Under the microscope some of the old sheathings show 
minute specks of what looks like filmy gold, they may be particles 
of bright muntz metal, which have been deposited on the crust of 
oxychloride, oxide and other compounds forming the scale, for 
Tass is deposited electrolytically ; on treatment with nitric acid 
they disappeared in the effervescence set up by solution or other- 
