BY H. W. FOX, ESQ. 149 
benefit of the uninitiated) that the usual portrait and lands- 
cape photographs are printed on a paper previously 
coated with a solution of nitrate of silver, and the silver 
unacted on by the chemical rays of light, having been 
dissolved out by dipping in a solution of hyposulphate of 
soda. This soda is removed as nearly as can be by 
repeated washings of pure water, but it is practically 
impossible to destroy or eradicate every trace of the soda 
from the pores of the paper, and the small portion which 
remains will eventually have a chemical action on the silver 
of the print, causing it gradually to assume the form of 
sulphate of silver, which is a dirty yellow colour. You 
may have noticed on some old prints yellow spots; they 
are the result of the soda still retained in the pores of 
the paper. Again the atmosphere, especially a damp one, 
may contain sulphates, which attack more or less such a 
sensitive as silver, causing a deterioration in colour. 
Nitrate of silver has been used with good permanent 
results on fabrics which have been kept in a very dry 
place, as in a dry atmosphere the sulphates are much more 
weak than in a damp one. And in such places as stone 
coffers in the centres of pyramids, dampness would be in 
the minimum. I have heard that the documents found in 
such places have been often written with the nitrate of 
silver. 
The nitrate of silver being so evanescent on paper has 
caused photographers to tax their brains to find a suitable 
substitute, in which they have been eminently successful, 
using a carbon pigment instead of the silver, thereby 
defying (within certain limits) the ravages of time. A num- 
ber of processes have been taken advantage of by some 
publishers of books for their illustration, but these cannot 
be brought into general use for portrait or landscape 
photography, as the prints could not be produced in small 
numbers at a cost suitable to the public, therefore the 
public must be contented as at present with ones that fade. 
Reference might be made to several of these carbon 
processes, viz., the Heliotype, Woodburytype, Albertype, 
Phototype, Photogravure, Photolithographic, &c., all of 
which are permanent. 
