

Metals and other Bodies on a Photographic Plate. Ill 



uric acid and afterwards, for three days, with, nilric acid, and the 

 picture it then gave was very faint, and on repeating this purifying 

 process no picture at all was produced. Again, a sample of mercury 

 containing zinc was carefully distilled. The distillate gave a very 

 faint but very distinct picture. Another sample of distilled mercury 

 also gave a faint picture. 



Temperature, as might be expected, affects greatly this activity 

 of the metals ; at 4 or 5 C. zinc has but little action on a photo- 

 graphic plate. Most of the foregoing experiments have been made 

 at about 17 or 18 C., and some, as specially noted, at 55 C. The 

 Ilford special rapid plates have been used. 



It appears, then, from the above experiments that certain metals 

 have the property of giving off, even at ordinary temperatures, 

 vapour which affects a sensitive photographic plate, that this vapour 

 can be carried along by a current of air, and that it has the power of 

 passing through thin sheets of such bodies as gelatin, celluloid, 

 collodion, &c., in fact, so transparent are these bodies to the vapour 

 that, even after it has passed through them, it is able to produce clear 

 pictures of the surface of the metal from which it came. That much 

 remains to discover with regard to this action of the metals is 

 obvious, the most active metals are not the most volatile. Nickel is 

 very active, cobalt only very slightly so, copper and iron are practically 

 inactive. I hope before long to be able to bring before the Society 

 further developments of these curious actions, both of metals and 

 organic bodies. 



The foregoing experiments have been made in the Davy-Faraday 

 laboratory, and I beg to thank the managers of the Royal Institu- 

 tion for having allowed me to work in their laboratory. My thanks 

 are also due to my assistant, Mr. Block, for the very careful and 

 intelligent way in which he has aided me with the experiments. 



March 24, 1898. Additional experiments have been made with 

 active organic substances, in order to determine to what class of 

 bodies they belong. As already stated, linseed oil and turpen- 

 tine were the two substances first found to be very active organic 

 bodies, and following out these results it has been proved that 

 vegetable oils in general have more or less this property of acting on 

 a photographic plate. Linseed oil, for instance, is very active, olive 

 oil only very slightly so. Even samples of " pure " linseed oil ob- 

 tained from the different artists' colourmen vary considerably in the 

 amount of action which they exert. The boiled, or drying linseed oil, 

 has, at ordinary temperatures, the same activity as the ordinary 

 oil, but under other conditions it appears there is some difference in 

 their action. Another class of bodies, also called oils, namely the 

 essential oils, have been found to be very active substances. 



