RECENT DISCOVERIES IN PHOTOGRAPHY. 
401 
In the meantime Mr. Stillman, who has done much for dried 
collodio-emulsions, and who has succeeded in making one of 
excellence and stability, is engaged in trying to solve the 
problem of conferring as much sensitiveness on the collodion 
pellicle as that at present possessed by gelatine. That he will 
succeed we have every reason to believe, judging by what we 
have seen in course of our experiments with him. A revolution 
in the practice of negative photography is rapidly being 
effected ; when a dried collodion emulsion shall have been 
obtained that will possess the sensitiveness of gelatine the 
revolution will be complete. 
Not alone in the production of negatives have discoveries 
been recently made. It has been a standing disgrace to photo- 
graphy that its prints faded ; their permanence could never be 
relied upon. Hence the endeavours to have silver printing 
supplanted by carbon or any other reliable substance. 
Starting with the idea of printing photographs in the most 
stable metals known, such as platinum or iridium, Mr. William 
Willis, jun., recently sought to find a good reducer of these 
metals, and spent some time in making experiments with 
ferrous oxalate, a beautiful lemon-yellow powder, known to be 
insoluble in water and most other menstrua. Working away 
for a time without any satisfactory result, he eventually dis- 
covered that a solution of it in the neutral oxalate of potash 
instantly precipitated the metal from the ordinary chloride of 
platinnm ; in other words, he found that a solution of ferrous 
oxalate in potassic oxalate reduced salts of platinum to the 
metallic condition. Now, as ferrous oxalate can be produced 
by the action of light upon ferric oxalate, it follows that if 
paper which has received a wash of chloride of platinum and 
ferric oxalate be exposed under a negative in the printing- 
frame, and then receive a wash of potassic oxalate, the metal 
will be reduced in proportion to the action of the light. 
When this printing process, the principle of which we have 
thus described, is carried out in actual practice, a picture of a 
fine quality is obtained by an exposure to light of about one- 
fifth of that required for ordinary silver printing ; that, at any 
rate, is the estimate we made when witnessing the process 
worked. When the pictures are taken from the printing frame 
they are feebly although distinctly visible, although up to this 
stage the platinum has not taken any part in the performance. 
The visible picture is composed of ferrous oxalate, and it would 
have been equally visible had no platinum been present. The 
picture is now drawn over a solution of potassic oxalate, and 
instantly, as the result of this contact, the image becomes 
strong and rich, of a warm velvety-black tone. 
As far as mere permanence is concerned the picture is now 
VOL. XIV. — NO. LVII. D D 
