on the Saline Contents of Sea-Water. 437 



sources of error, it is necessary to operate upon pure sea- 

 water, and not upon salts obtained from it by the usual pro- 

 cesses in the large way, these being always more or less con- 

 taminated 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, aiul the evaporation which it had under- 

 gone at Portsmouth had onh' separated from it a quantity of 

 calcareous matter, principall}- 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 olij 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 least acted upon, nor was any smell of nitric acid per- 

 ceived ; but on adding the smallest quantity of nitre to the 

 same mixture, the gold was dissolved, and the smell of aqua 

 regia was instantly perceived f. 



A portion of the said bittern was next examined by appro- 

 priate re-agents with a view to detect any minute quantity of 

 earths or metals, esj^ecially alumina, silica, iron and copper, 

 which former incpiirers might have overlooked : but I could 

 find no othei- earth except magnesia: and to my siu'prise, I 

 did not find in the bittern the least particle of lime ; which 

 proves that sea-water contains no nuniate of lime, as had been 

 generally supposed. I was equally unsuccessful in my at- 

 tempts to detect iron or copper, by the most delicate tests. 



* The water, immediately on being raised from the Rca, had been allowed 

 to stand a siifTiLicnt time to deposit the earthy |)articles suspended in it, 

 by which means it had i)ccome Ijeantilully transparent. 100 |)onnds of 

 the water produced only three fjrains of earthy sediment, in wiiicii I could 

 discover nothing l)ut carbonate of lime and oxide of iron. It is in this sedi- 

 ment, according to llouelle, that mercury is to be found. I need iiardly say 

 that I could not detect in it the least particle of that metal. 



f For this easy and elegant process for dete<ting nitric acid, a point at- 

 tended with difficulty, I am indebted to Dr. WoIIaston. 



In 



