The Dogs Mercury was at one period thought to be an innocent plant, its poifonous qualities were 
dilcovered by accident : the Annual, or French Mercury, has, at prefent, the reputation of being not only 
harmlefs, but to poilefs medicinal virtues ; it is of fome confequence then for us rightly to diftinguilh the two 
and in this there is little difficulty. The Dogs Mercury has a flrong, creeping, perennial root; this an 
annual one . the Dogs Mercury flowers only in the Spring ; this the whole Summer long : the Dogs Mercury 
has an unbranched item ; this a ftalk branched down to the bottom. ° 
The Annual Mercury has been ranked among the emollient oleraceous herbs; it is faid gently to loofen 
the belly -, its principal ufe has been in glyflers. 
The whole plant, particularly when in flower, has a flrong fmell of Elder. 
The fine blue colour which the Dogs Mercury acquires in drying, has induced feveral perfons to believe, 
that the plant, if properly treated, might be made, as well as many others, to produce Indigo : this induced 
Mr. Macintosh, an ingenious young gentleman of Glafgow, to make the following chemical analyfis of it, 
with which he was fo obliging as to favour me ; and though it does not come under the proper plant, we 
apprehend no apology will be neceflary for inferting it here. 
“ The whole plant, on being put into water, gives out a fine blue colour, which is immediately changed 
into a green by the addition of an alcali ; but an acid has not the power of changing its colour into red, 
“ as it does moll blue liquors, it only weakens the blue, and if a large quantity be added, it nearly deftroys 
“ it. The whole plant, on being dried, aflumes a blue colour, which it gives out readily to water; but in 
“ ca fes, if a boiling heat be ufed, it only acquires a deep dirty green, which changes gradually into a 
brownifh red. Upon agitating violently the blue liquor, I always found it was changed into a brown 
“ colour, the blue being entirely loft, and not to be recovered by any means I could fall upon. There falls 
“ during this procefs, a fmall quantity of precipitate, which is alfo brown. If the blue liquor be evaporated, 
“ the whole is likewife changed into the fame brownifh colour, and a fimilar precipitate falls, which, on 
“ being put into water, gives it a dark red colour. Newly-flacked lime put into the blue liquor, firft 
“ changes it into a green, which is very foon after deftroyed. I have obferved in the beginning of the 
“ evaporation, a blue fecula upon the fides of the veflel, but always before the end of the procefs, the whole 
“ was of the brownifh colour mentioned above.” 
