On the Art of Hardening Copper. 47% 
the eye, and the filver the tongue, the communication being 
eftablifhed as before with copper *. 
' In regard to the hydrogen of the decompofed water,’ the 
author thinks that it may alfo be abforbed by the metal: he 
even confiders as ari hydro-oxyde of tin, the o¢taedral cryftals 
which he remarked on the furfaces of the pieces of tin em- 
ployed in thefe experiments.—It is clearly feen, fays C. Fab- 
broni, by the refults which I obtained from the fimple con- 
taét of two metals in water, that is to fay, by the oxyde and 
faline cryftals, that a chemical operation takes place, and that 
to it we ought to afcribe the fenfations experienced on the 
tongue and by the eye. It appears to me, then, probable, 
that it is to thefe new compounds, or their elements, that we 
are indebted for that myfterious ftimulus which produces the 
convulfive movements of the animal fibre in a great part at 
leaft of the galvanic phenomena. 
XI. On the Art of Hardening Copper. By P.1. Hieum f. 
Corprn: in its pure and perfeé ftate, is exceedingly 
foft and malleable: its toughnefs is then fo great, that it is 
exceeded only by gold and iron. When copper is hammered 
a long time cold, and {till more when rolled, it is found, as 
is well known, fomewhat harder than before, but it does not 
- thereby acquire that ftrength which deferves the name of 
hardening, or which enables it to make fuffictent refiftance to 
{trong imprefiions. By being brought to a bright-red heat 
in the fire, and fuddenly quenched in water, copper obtains 
no perceptible addition to its hardnefs; but, on the contrary, 
becomes more pliable, and confequently fofter than before. 
If the copper is kept a long time in fufion, or often fufed in 
a {trong heat, without any covering of flux or charcoal pow- 
der, it becomes brittle and unmalleable, and confequently 
_ * This is no conclufive argument againft the effet being electrical ; 
it is taking for granted that the laws and properties of the eleétric fluid 
_ have all been afcertained. Epur, 
» + From Tian/udtions of the Ruyo! Acaiemy of Sciences at Stockholm for 
1797+ . é, 
ot. harder: 
