Said ti 
XIV. On the Discoloration of Silver by a hard-boiled Figg. By 
Mr. J. Murray, Lecturer'on Experimental Philosophy. 
London, Qtst Jannary, 1814. 
Sirs, Tue discoloration, of silver by a hard-boiled egg is a 
question difficult of solution. It may appear to be an anomalous 
phenomenon. : 
Observation and experiment enable me to state the following 
circumstances : 
If ‘a slip of polished silver permeates the albumen of the egg 
exclustvely, it suffers no change ; but if it also penetrates the 
yolk, itis instantly tarnished, and (what is worthy of particular 
remark) the siraium of the metal in contact with the allumen 
dlone is coloured, while the surface of the silver embraced by 
the yolk retains its pristine lustre and character. ‘The effects 
are more imposing, ii the silver be suffered to pass through the 
first stratum of albumen, then through the yolk, and then again 
through the albumen. The impression is also more sensible the 
harder the egg. f 
There are two views in which the phenomenon may be consi- 
dered; Ist, an clectrical phenomenon ; 2dly, a chemical effect : 
—if the former, which I conceive it to be, then it is a modifi- 
cation of that Voltaic circle which Davy announces, and where 
one metal is concerned. In the present case, however, there is 
only one menstruum, namely the yolk furnishing saulphuretted 
hydrogen. The effect produced at each end of the silver, it fol- 
lows from hence, must be a positive phenomenon, The albu- 
men is decomposed, and the olive oxide of silver produced, 
compounded according to Davy of 100 parts silver and 7-3 parts 
oxygen. 
Were it the su!phuret of silver, it ought to be tarnished only on 
that part of the slip which the yolk envelops. It receives the 
oxygen, according to my estimate of the phenomenon, from the 
albumen, which is known to contaia it. ' 
“ Si quid novisti re: tius istis, 
Candidus imperti.” 
I may again revert to the subject. 
I observe that Mr. Walker of Lynn has, in No. 187, page 368, 
of The Philosophical Magazine, given a theory of combustion as 
deduced from Galvanic plienomena. In my lecture on Galvanism 
at Lynn, I took occasion to point out that there were two opi- 
nions respecting the evolution of oxygen and hydrogen at the 
respective poles of the Voltaic circle: Ist, Resting on the sup- 
position that water is composed of hydrogen and oxygen, that a 
decomposition might take place, and these constituents be libe- 
rated 
