180 
NOTES AND QUERIES. 
fond §, No 9,, Man, 1, '56. 
sub-chloride of silver, as has ustially been supposed; that 
this silver, by contact with the baths above mentioned, is 
transformed into sulphide of silver, which is afterwards 
modified by the vapours in the atmosphere. Experience 
has proved the correctness of this hypothesis. 
To verify this analytically, MM, Davanne and Girard 
endeavoured to ascertain firstly, what was the state of the 
silver in the positive, fixed, and not toned, examining in- 
cidentally if there remained any hyposulphite of soda in 
the substance of the paper. Secondly, what was the state 
of the silver on 2 positive proof toned in the usual way, 
that is to say, by means of the hyposulphites charged 
with chloride of silver or acetic acid, those baths which 
photographers call old hyposulphites. The process which 
they employed to effect this analysis was very simple; it 
consisted of impregnating the sheet of paper with a solu- 
tion of nitrate of potash and carbonate of soda, burning it 
and submitting the ashes to analysis; after the calcina- 
tion, the silver remained in an insoltible state, whilst the 
chlorine and the sulphur were transformed into chloride 
and sulphate. The accuracy of this process was first veri- 
fied by burning a sheet of paper impregnated with chloride 
of silver, and determining the quantity of silver in the 
ash by chlorine, and the quantity of chlorine by means of 
silver, and weighing the two precipitates of chloride, they 
were found to be identi¢al. In the same way the com- 
position of the ash of photographie paper was deterniined, 
with a view to further analyses. 
To decide the first question, a sheet of paper, impreg- 
nated with chloride of silver, was completely blackened 
by exposure to the light, washed in fresh hyposulphite of 
soda, then in distilled water, and finally burned; no trace 
of sulphate was found inthe ash. The quantity of chlorine 
amounted to 0-002 grammes; that of the silver to 07124 
grammes. It was evident from this, in the first place, 
that the fresh hyposulphite of soda had left no trace of 
sulphur, and in the next place, that the proportion of 
chlorine was so small compared with that of the silver, 
that it might be considered as an impurity in the paper; 
the formula Ag. » Cl. would have required ten times as 
much, that is to say, 0-020 grammes. Several times 
repeated, this analysis always gave the same results. 
But before drawing a conclusion, MM. Davanne and 
Girard wished to give it a more palpable form. They 
prepared a considerable quantity of chloride of silver, and 
spread it in a capsule, and exposed it to the light of the 
sun for a whole day, stirring it continually; it was 
washed with hyposulphite of soda, then with distilled 
water, and the residue, fused with pure carbonate of soda, 
gave a button of metallic silver, but the flux did not 
contain any traces of chlorine. It must be ‘added, that 
the surface of a photographic print is perfectly soluble in 
acetic acid, whilst the sub-chloride is considered insoluble. 
From these experiments, it may be concluded that the 
positive photographic image is formed by metallic silver, 
and not by sub-chloride of silver, as has been hitherto 
supposed. 
To determine, in the next place, what was the state of 
the silver on the toned proofs, they analysed a cer- 
tain number, on which the desired black tints had been 
produced, by means of the ordinary toning baths (hypo- 
sulphite of soda mixed with acetic acid, or salts of silver), 
and not only was silver always found, but sulphur also; 
these two substances occur together almost in atomic 
proportions, such as are required in the formula Ag. S. 
This result is continually reproduced, and we may there- 
fore conclude, that in the above-mentioned toning baths, 
the silver with which the paper is covered is transformed 
into sulphide,—a reaction easy to comprehend when we 
recollect that the hyposulphites are immediately decom- 
posed by acetic acid, and, as experience bas shown, these 
salts mixed with a solution of nitrate of silver are trans- 
formed almost instantaneously into sulphide of silver. 
Proceeding fromthis to the study of prints that had 
suffered a change, they submitted to analysis some that 
had been prepared several years ago; and of which the 
black colour had been transformed into yellow; these 
they had prepared themselves, and had washed them for 
several days with water, after coming from the toning 
bath; and also others that they had directly sulphurised. 
In each case they found sulphur and silver, and, what was 
curious, the proportions were the same as in the black 
prints coming from the toning bath. 
It seems to be clear, therefore, that in ptints that have 
merely been fixed, analysis indicates only the presence of 
silver, while in those that have been toned, whether they 
are black or yellow, there is both sulphur and silver, and 
these substances only. It remained to be seen whether 
this sulphuration was really the cause of the destruction 
of the image. In order to determine this, they sulphurised 
properly fixed prints, both by the photographic process, a 
bath of hydrosulphuric acid, and a current of sulphuretted 
hydrogen, and in every instance where the sulphurised 
prints came in contact with moisture, the black tones 
rapidly disappeared and gave place to vellow, while those 
prints that had merely undergone the fixing process 
showed no change. 
The conclusion which MM. Davanne and Girard de- 
duce from this is, that sulphuration is the cause of the 
toning, and, in the presence of moisture, causes the de- 
struction of the print. But that the employment of the 
salts of gold, which give rise to a totally different re- 
action, is productive of no mischief, 
The question still remains to be investigated, why the 
black sulphide of silver becomes yellow in the presence of 
moisture. As there is no change in the proportion of the 
elements constituting it, we are forced to admit, either a 
hydration of the compound, or an isomeric modification, 
analogous to the red and black sulphides of mercury. 
In conclusion, they state, that it is easy, when a print 
has become faded, to restore the black tones, which may 
be augmented or diminished at pleasure. All that is 
necessary is to immerse it for a few hours, and in the 
dark, in a bath containing two or three grammes of ter- 
chloride of gold to a litre of water; a double decomposi- 
tion takes place, and the gold is deposited in the place of 
the silver. The chloride of silver formed, is then re- 
moved by a weak solution of hyposulphite of soda and the 
print washed; the picture will be found to be completely 
restored, 
Replies ta Minor Gueries. 
“ Myrrour of the Worlde” (2° S. i. 153.) — 
As I possess a copy of the second edition of this 
work mentioned by you, a volume also of the 
greatest rarity, if Mr. Kensineton would like to 
compare it with his imperfect copy of the first, it 
will give me much pleasure to show it him; and 
I should also be gratified by a sight of the one in 
his possession. My address is No. 6. St. Mary’s 
Place, West Brompton, and perhaps he will kindly 
communicate with me on the subject. The actual 
comparison of copies of these very early printed 
books is of great importance. J. O. Hanurwett. 
“ The Wanderer and Traveller” (2° S. i, 94.) 
—The author of Zhe Wanderer and Traveller 
