260 On the Connexion which exists between 
sized plates (about a quarter of an inch diameter) in tubes 
with ivory caps, make: very neat pocket instruments, and 
are sufficiently powerful to move a small ivory needle 
suspended on a point. I remain, &ce. 
B. M. Forster. 
« 
XXXV. Memoir on the Connexion which exists between 
the Oxidation of the Metals, and their Capacity of Satu- 
vation for the Acids. By M. Gay Lussac*. 
Ir has been Jong known that there are some metals which 
precipitate other metals from their acid solutions in the 
metallic state. Bereman had remarked, expressing him- 
self according to the chemical theory then adopted, that 
the phlogiston of the precipitating acted on the precipitated 
metal, and Messrs. Sylvester and Grothuis have besides 
shown, that when precipitation has once commenced by 
a chemical affinity, it may continue by a process purely 
Galvanic. Nevertehless the chief phenomena which ac- 
company this precipitation have escaped the attention of 
chemists. We are ignorant, in particular, of the relation 
which subsists between the quantity of the metal precipi- 
tated and that of the precipitating metal; and of course 
we are ignorant of the important consequences which flow 
from it. I propose to determine this relation, and to prove 
that the quantity of acid which the various metals require 
to saturate them is in a direct ratio to the quantity of oxy- 
gen which they contain. I have arrived at this principle, 
not by the comparison of the known proportions of the 
metallic salts, which are in general not so very exact as to 
enable us to recognise any law, but by observing the mu- 
tual precipitation of the metals from their acid solutions. 
When we precipitate in fact a solution of acetate of lead 
by a piece of zine, a beautiful vegetation is formed known 
by the name of arbor Saturni, and which is owing to the 
reduction of the Jead by a Galvanic process. We obtain 
at the sanie time a solution of acetate of zinc equally neu- 
tral] with that of Jead, and entirely exempt trom this last 
metal. Little or no hydrogen 1s extricated during the pre- 
cipitation ; which proves that the whole of the oxygen ne- 
cessary to the zinc for dissqlving and saturating the acid 
has been furnished to it by the lead. 
If we put into a solution of sulphate of copper slightly 
* Mem. d’Arcueil, tome ii. p. 159. , 
.. acid 
