452 Dr. Marcet’s experiments and researches 
water, and not upon salts obtained from it by the usual pro- 
cesses in the large way, these being always more or less 
contaminated by the clay pits in which the evaporation is 
carried on, by the metallic boilers, or other adventitious causes. 
I therefore now turned my attention to the sea-water itself, 
and in particular the perfectly pure and transparent specimen 
of concentrated brine from the Channel, which I have above 
mentioned. Mr. Barry procured this water near Bembridge 
floating light, about two miles N. E. of the eastern extremity 
of the Isle of Wight, and the evaporation which it had un- 
dergone at Portsmouth, had only separated from it a quantity 
of calcareous matter, principally selenite.* 
A few pounds of this water were evaporated nearly to dry- 
ness, at a gentle heat, so as to reduce the mother liquor to the 
smallest possible quantity. This liquor was suffered to drain 
off, and reserved for experiments, as it is in this fluid that 
any new ingredients are most likely to be detected. 
I had suspected that some nitric salt might be found in sea- 
water, but in this I was disappointed. The discrimination by 
the shape of the crystals being in this instance scarcely prac- 
ticable, the mode which I employed for detecting it, consisted 
in concentrating the bittern in a glass tube or retort, till it 
began to deposit solid matter, then adding sulphuric acid and 
gold-leaf, and boiling the mixture ; the gold-leaf was not in 
* The water, immediately on being raised from the sea, had been allowed to stand 
a sufficient time to deposit the earthy particles suspended in it, by which means it 
had become beautifully transparent, ioo pounds of the water produced only 3 
grains of earthy sediment, in which I could discover nothing but carbonate of lime 
and oxide of iron. It is in this sediment, according to Rouelle, that mercury is to 
be found. I need hardly say that I could not detect in it the least particle of that 
metal. 
