34 M. C. Lea—Combination of Silver Chloride 
formations of the United States have not afforded as yet any 
records of land plants earlier than those of the Lower Devonian. 
o and Kentucky, vegetable remains of this kind have 
been fontnd at different places, mostly in concretions, including 
the section of the Araucarie, together with eae pA 
plants; Stgmaria, Sigillaria and “Lepidodendron. In Pennsyl 
vania, a Lepidodendron, L. primevum Rogers, and a Sigillavia 
have been ctutaisiid from the same horizon. These fragments 
reas yet rare, and have not been satisfactorily determined, on 
account of the imperfect character of the specimens, mostly 
petrified pieces of wood, whose structure is studied with difii- 
culty. It is certain, however, that in the Middle Devonian we 
have representatives ‘of three distinct groups of vegetables: the 
Cellular Cryptogams, in a quantity of marine plants, the sie 
cular Cryptogams, in Lycopodiaceous plants: Lepidoden 
Siyillaria, etc., and the Phenogamous Gymnosperms, in "the 
Conifers. 
Art. IX.—On a Combination of Silver Chloride with Mercuric 
Iodide; by M. Carry Lua, Philadelphia. 
a ci. course of an extended examination of the compounds 
formed by mercuric iodide, I some time since obtained two 
ay I believed to be new. After having studied their pro- 
perties, 1 found that one of them, a compound of the iodides of 
silver and of mercury, had previously been obtained by Meusel. 
I shall therefore bere describe only the compound which mer- 
euric aan forms with silver chloride. 
rtion of recently precipitated and still moist silver 
aoe a considerably less quantity of mercuric iodide, also 
freshly precipitated and still moist, be added, we shall find that, 
after stirring them thoroughly to gether, the scarlet color of the 
mercuric salt is still plainly visible through the mass, which is 
of a bright salmon color. By standing some hours or a day, a 
remarkable change takes place, the red color wholly disappears 
and the powder became pure lemon-yellow. Before this change 
took place, the separate particles of the mercuric iodide could 
be plainly distinguished with a lens; after it, the powder be- 
comes perfectly homogeneous. Fresh portions of mercuric 
iodide yee gradually disappear in the same way, until an 
equivalent quantity has been used. 
A better plan, however, for popes the aren consists in 
adding to a solution of a weighed quantity tassic iodide an 
exactly equivalent quantity of mercuric ¢ Be, e, and then, after 
thoroughly agitating and allowing the precipitate to fall, adding 
