262 Dr. Manet's Experiments and Researches [April, 



confirmed that statement, by announcing that he had found 

 traces of mercury in all the specimens of marine acid which he 

 had examined. 



Improbable as the fact appeared, I thought it worth while to 

 repeat the experiment, and to take that opportunity of making- 

 some collateral researches upon other substances, much more 

 likely than mercury to be discovered in sea water. 



For this purpose I availed myself of the kindness of my friend 

 Mr. John Barry,* who happened to be in the vicinity of Ports- 

 mouth, to supply me with specimens of sea-water, carefully con- 

 centrated upon the spot, in vessels of Wedgwood ware, and with 

 scrupulous attention to cleanliness in the process. Accordingly 

 he was so obliging, as not only to send me a quantity of brine 

 evaporated under his own eye, in the manner just mentioned, 

 but he also collected for me a valuable series of specimens from 

 the salt works near Portsmouth, from all the stages of the pro- 

 cess, so as to afford me an opportunity of investigating with 

 accuracy all the chemical circumstances of this interesting 

 branch of national economy. Finding myself, however, much 

 pressed by time at this late period of the session, I shall, after 

 briefly adverting to Rouelle's supposed discovery, confine 

 myself in this communication to a few observations which I have 

 made on sea-water itself; keeping out of view, for the present, 

 the topic of salt-making, which, however, I intend to resume at 

 some future period, in a more complete and satisfactory manner. 



I first attempted to detect mercury in a specimen of bay-salt, 

 such as is obtained in the salt-works near Portsmouth, by spon- 

 taneous evaporation. This variety of salt forms large crystals, 

 but is always more or less contaminated by earthy matter, 

 which gives it a dirty appearance. It has, probably, a general 

 resemblance to the French Sel de Gabelle, which is more impure 

 still, though, I believe, obtained in a similar manner.f 



Eight ounces of this salt were put into a coated retort con- 

 nected with a receiver, and about four ounces of nitrous acid 

 were poured upon it. A pretty brisk action took place, which 

 was further increased by the application of heat ; fumes of chlo- 

 rine were immediately disengaged, and a reddish fluid condensed 

 in the receiver; the heat was continued, and gradually raised in 

 a charcoal fire till no acid or moisture any longer came over ; at 

 which time a new emission of red fumes indicated that the 

 nitrate formed in the retort was beginning to part with its acid : 

 minute drops of fused salt soon bedewed the upper part and 

 neck of the retort, so as to be mistaken at first for a sublimate. 

 This, however, proved to be almost solely muriate of soda ; and 



• Mr. John Rarry, of Plough Court, inventor of a new and valuable process for pre- 

 paring extracts in vacuo, &c. 



-f- The name of bay-salt is often applied to foreign as well as British salt, and in 

 general it simply denotes that the salt has been obtained by spontaneous evaporation. 



