438 Scientific Proceedings, Royal Dullin Society. 



The reverse process was also tried, namely, to change the sign of the 

 gelatine of the film, but it was found that plates soaked in a solution of barium 

 nitrate were no more easily sensitized than untreated ones. 



The influence of the physiological condition of the chlorophyll itself was 

 also tested ; thus extracts from leaves recently exposed to light were compared 

 with those made from leaves previously shielded from light. No difference 

 was observed. In the same way extracts made and stored in darkness showed 

 themselves no different from those which had been exposed to the light. 



These preliminary experiments afforded no hopes that certain results 

 could be readily obtained with gelatine photographic plates. Consequently 

 it was decided to abandon gelatine films and to carry out the experiments with 

 collodion emulsion in spite of its inconveniences. 



It was noticed, however, that in the occasional cases in which satisfactory 

 sensitization was obtained with gelatine plates it was effective, not only at 

 room temperature, but was also observed on portions of the same plates 

 exposed under liquid air. 



Experiments on the Sensitization of Collodion Films. 



The first experiments which we made with collodion were carried out with 

 an emulsion made up in the laboratory. The plates, which were coated and 

 allowed to dry for about five minutes, were then immersed in a leaf-extract. 

 Subsequent drying lasted half an hour, and then the plate was exposed to 

 light, as previously described in the case of the gelatine films, at room 

 teinperature for sixty to eighty seconds. Sensitization was easily obtained 

 both with ordinary dry-leaf extract and with an alcoholic solution of 

 chlorophyll a and b purified from the accompanying yellow pigments and fats. 



With exposures for thirty minutes and sixty minutes under liquid air the 

 result was inconclusive, as the whole plate appeared somewhat fogged, and 

 no clear strip corresponding to the shadow of the band was observed. 



Similar collodion plates sensitized with "Sensitol Eed " in a similar manner 

 gave good results, both for room temperature and when submerged in liquid 

 air. At room temperature (as in the case of gelatine plates) the effectiveness 

 of the sensitizer, as shown by the contrast between the sensitized and 

 untreated portions of the plates, was much greater. 



Further experiments were carried out, using a sample of collodion prepared 

 and supplied by Messrs. Johnson & Sons, Finsbury, London. The coated 

 plate after five minutes' drying was partially immersed in leaf-extract. After 

 this immersion it was again allowed to dry for ten to fifteen minutes. Exposure 

 to light for three hours was Chen made while the plate was submerged in 



