SCIENTIFIC SUMMAKY. 
383 
any modification of the old silver process, which they have now wrought up 
to such a pitch of perfection. This fading has been pretty clearly shown to 
be, at least mainly, due to the action of the hyposulphites. The print lasts 
a longer or shorter time in proportion to the degrees in which the fixing- 
agent — hyposulphite of soda — has been removed from the paper ; but the 
slightest trace of it will assuredly bring about the destruction of the photo- 
graph. The only chance of absolute permanence appears to be in its com- 
plete elimination, although even then there are other elements of evil which 
may be suspiciously regarded. We have hitherto relied for this purpose 
upon the mechanical action of water, and some able men have run counter to 
the general experience by affirming that absolute permanence could be ob- 
tained by proper and sufficient washing. Mr. Carey Lea, for instance, 
asserted, about a year since, that he had tested properly-washed prints with 
a very delicate and certain test for the hyposulphites without discovering 
their trace, and in prints which he considered had been properly washed. 
This test was that of placing a few drops of an alcoholic solution of iodine in 
several ounces of water, and applying the same with a camel’s hair brush to 
photographs on starch-sized paper. The presence of the starch, if freed from 
the hyposulphite by sufficient washing, was indicated by a violet or purple 
stain where the solution was applied ; but in prints not thus washed the 
presence of the hyposulphite was indicated by the absence of such stain, 
which could be at once removed from the well-washed print by plunging it 
into a solution of alkaline hyposulphite. On the other hand, Mr. Dawson, 
of King’s College, in a recent number of The British Journal of Photo- 
graphy , denies the power of mere washing to give permanence, “ unless 
the prints have been soaked for some time in hot water so as to remove all 
the size — even then, supposing the paper non-albumenized, — the elimination 
of the whole of the hyposulphite is problematical.” He adds, — “ Some pho- 
tographers, we are aware, do treat their prints with a final wash in hot water ; 
but this, of course, although unquestionably conducive to. the permanence 
of the proof, does not remove the whole of the size in which the hypo- 
sulphite is locked up ; and if it did, the paper would be as little cohesive as 
blotting-paper, and the prints would lose much in vigour and brilliancy. In 
the case of prints on albumen, or albumenized paper, hot water, we may 
reasonably suppose, has no more powerful effect in removing hyposulphite 
from albumen than cold water, if, indeed, it has so much ; and it can only be 
by acting on the texture of the paper itself, and removing the size therefrom, 
that it can exercise a beneficial influence at all.” To demonstrate the truth- 
fulness of his ideas on this subject, some prints which had been washed in 
cold running water, and with the utmost care and attention for over twenty 
hours, — and the final drippings from which, when subjected to the tincture of 
iodine test, displayed no trace of the hyposulphite, — were experimented with, 
and still gave up to boiling water, in which they were steeped, at least 
one-fortieth part of a grain of the destructive element to the half-sheet of 
paper, clearly showing that the cold water had not really removed it all, 
although it had eliminated all that it could reach or had influence over. Now 
whether Mr. Dawson and his supporters or Mr. Lea and his supporters be right, 
whether photographs fade so universally because they are rarely or never 
sufficiently washed after the process of fixing, or because it is impossible to 
