183 
‘ Hyposulphite of silver. — Muriate of silver newly precipitated 
is soluble in all liquid hyposulphites, and, as before observed, in 
that of soda with great ease and in large quantities. This solution 
is not accomplished without mutual decomposition, as its intense 
sweetness proves — a sweetness surpassing that of honey, and dif- 
fusing itself over the whole mouth and fauces, without any 
disagreeable or metallic flavour.” (p. 27.) 
In a second paper on the same subject, which appeared in the 
same jonmal, vol. 1, p. 396 et seq., it is shown ( inter alia) that the 
affinity of this acid for silver is such that oxide of silver readily 
decomposes hyposulphite of soda and likewise the soda in a caustic 
state, “ the only instance, I believe, yet known of the direct dis- 
placement of a fixed alkali vid humidd by a metallic oxide.” 
(p. 397.) 
“ Hyposulphite of ammonia and silver. — Its sweetness is unmixed 
with any other flavour, and so intense as to cause pain in the 
throat one grain communicates a perceptible sweetness to 
30,000 grs. of water.” (p. 399.) 
In a third communication, dated November, 1819 — “The habi- 
tudes of this acid with the oxide of mercury are not less singular 
than its relation to that of silver.” — “ The red oxide is readily 
dissolved by .... , hyposulphite of soda, while the alkali is set at 
liberty in a caustic state,” &c. &c. 
The very remarkable facts above described I have reason to 
believe attracted a good deal of attention at the time, and thence- 
forward the ready solubility of silver salts, usually regarded as 
insoluble, by the hyposulphites was familiar to every chemist. 
It would not therefore be surprising if Daguerre tried it to fix 
his plates ( i.e . to wash off the iodide coating); but I have been 
informed, though I cannot cite a printed authority for it, that at 
first he fixed with ammonia, or with a strong solution of common 
salt. 
For my own part the use of the hyposulphites was to myself the 
readiest and most obvious means of procedure, and presented itself 
at once. My earliest experiments were made in January, 1839, 
and in my notebook I find : — 
“Exp. 1012. — 1839, Jan. 29. Experiments tried within the 
