450 Dr. Marcet’s experiments and researches 
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 crys- 
tals, but is always more or less contaminated by earthy mat- 
ter, 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.* 
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 farther increased by the application of heat ; fumes of 
chlorine were immediately disengaged, and a reddish fluid 
condensed in the receiver; the heat was continued, and gra- 
dually 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 on careful exami- 
nation, it did not appear to contain the smallest atom of 
corrosive sublimate. 
1 next dissolved five or six pounds of bay-salt in water, 
and collected in a filter the insoluble earthy sediment, in 
* 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 evapo- 
ration. 
