ARGENTINE COMPOUNDS, SPREAD ON PAPER, SENSITIVE TO LIGHT, ETC. 331 
23. By plunging a paper washed with the solution of the nitrate of silver into a 
very diluted volume of sulphuretted hydrogen, and transferring it from thence into 
pure gas, a tolerably perfect surface is generally obtained. 
The continual plague of this process is, the want of perfect uniformity in the texture 
of the paper, which will often, in spite of every care, occasion an unequal absorption 
and thus mar the effect. 
24. Having tried every variety of paper I could procure, and finding all more or 
less objectionable, I had recourse to sizes of almost every variety. The difficulty 
was not, however, overcome by any of them ; the one which answered best was starch, 
which has the very singular property of altering the general appearance of that por- 
tion of the picture which is formed by the mercurial vapour when it is immersed in 
solutions of the muriate, or hyposulphite of soda, destroying the downy appearance, 
and giving it a sheeted silvery one. 
25. The experience gained by preparing these sulphuretted papers on an extensive 
scale, enables me to point out a method by which most of the defects arising from the 
inequalities of the paper, and its different rates of imbibition, may be overcome. 
The paper is to be first soaked in a weak solution of the muriate of ammonia, care- 
fully wiped with cotton cloths, and dried slowly. It is then to be dipped in a very 
dilute solution of the nitrate of silver, and the small bubbles which form on its sur- 
face to be carefully removed with a camel’s-hair pencil. When the paper is dried, 
which must be done in the dark, it is to be exposed in a closed vessel to sulphuretted 
hydrogen, slowly formed from the suiphuret of antimony and hydrochloric acid : in 
a few minutes it will darken to an iron brown. The paper must now be passed 
through water slightly impregnated with chlorine, or hydrochloric acid, and again 
dried. It must then be immersed in a solution of silver rather stronger than the first, 
and dried, whether in the light, or otherwise, appears of little consequence, care being 
taken that no shadow falls on the paper, as some difference exists between the shaded 
and exposed portions ; but the sensitiveness changes in a singularly uncertain way 
from the one to the other. It is to be again subjected to sulphuration, and by 
careful management the process is now generally completed. If, however, the paper 
is not considered as sufficiently dark, it must be once more washed in the solution of 
silver, and again subjected to the action of sulphuretted hydrogen. 
26. If the above muriated paper (25.) be allowed to remain in the sulphuretted 
hydrogen gas after the maximum blackness is produced, it is again whitened with 
some quickness. This may be accounted for in two ways ; the gas may be mixed 
effect is not produced by all pencils on the same paper, as a preparation of the paper, nitrate of silver over 
borax, seemed to succeed best. 
Gold-leaf printing (the common ornamental printing on cards, &c.) may be copied on nitrated paper, by 
simple juxtaposition and gentle pressure for some time in the dark, which is probably owing to the copper 
used as alloy, as the other may be by sulphur in the pencil. — J. F. W. H. 
2 u 2 
