416 Dr. W. j. Russell. On Hydrogen Peroxide as the 



so there is no doubt that hydrogen peroxide can readily pass through 

 a porous body by the aid of water. 



Alcohol acts in the same way as water, for when plaster of Paris 

 wetted with peroxide solution was poured into a couple of similar 

 dishes and allowed to set, and over one a piece of dry and over the 

 other a piece of Bristol board moistened with alcohol were placed, and 

 sensitive plates above them, after fifty minutes only a very faint 

 picture was formed above the dry board, but a claik one over the 

 wetted board. 



Celluloid is however nearly as transparent to these actions as gelatin, 

 find water in this case cannot be the transmitting medium, so that the 

 question is whether there be any constituent of the celluloid which 

 may act in a similar way to that of water in the gelatin. From the 

 following experiments it seems that camphor can do so : 



Camphor itself like water is a perfectly non-active body. To obtain 

 a thin non-porous layer of this body is difficult, but it is easy to prove 

 that the emanations from hydrogen peroxide solutions, from zinc, 

 copal, or other active bodies, are readily absorbed by it, and readily 

 pass through it. For instance, if a piece of camphor be placed 

 about quarter of an inch above a 2 per cent, solution of hydrogen 

 peroxide for seventeen hours and be then removed and placed on a 

 sensitive plate for fifteen minutes, it gives a dark picture, and when 

 a similar experiment is made using drying oil in place of the 

 peroxide solution, and the camphor be exposed to its action for 

 three days and then brought in contact with the sensitive plate 

 for one day, a dark picture is produced. This action can however be 

 easily carried still further and proved to pass through even a thick 

 layer of camphor. A piece O137 inch thick was placed about ~ inch 

 above a 2 per cent, solution of peroxide in a dish, for sixty-six hours, 

 and a sensitive plate placed on the top of it ; on treating this photo- 

 graphic plate with the developing solution it was found that a con- 

 siderable amount of action had occurred. Thus the camphor which is 

 a principal constituent of celluloid may enable hydrogen peroxide to 

 pass through it. 



That guttapercha and pure india-rubber should allow the action to 

 pass through them is remarkable. The substance known as guttapercha 

 tissue has a thickness of about 0*003 inch, and allows the action to pass 

 readily through it ; in fact, if even two thicknesses of this tissue be 

 placed over the 2 per cent, solution of the peroxide for seventeen 

 hours, a dark picture is obtained. If the tissue be laid on a polished 

 piece of perforated zinc and a sensitive plate above it, after remaining 

 there for a fortnight a fairly good picture is obtained. If drying oil be 

 used, the action will pass through the guttapercha in three days. 

 With regard to this transmission of the action, although the chemical 

 constitution of guttapercha is not well established, it is said to be a 



