Manchester Memoirs, Vol. Ix. (1916), No. 9. 13 



a history of the process and done some interesting work 

 himself, both with regard to the bleaching and the sensi- 

 tising of the dyes. Dr. Gebhardt has also published some 

 useful work upon the nature of the action of light upon 

 dyes, and the treatment of the dyes to render them more 

 stable. Dr. Stobbe (14) also published some interesting 

 work with regard to the action of light upon dyes a few 

 years ago. 



In 191 3 Dr. Alex. Just (15) discovered a new sensi- 

 tiser, di-ethyl-allyl-thio-urea, which for a certain group of 

 dyes sensitises about three times more energetically than 

 thiosinamine (allyl-thio-urea). Unfortunately it has not 

 been found applicable for sensitising all the dyes required 

 in a bleach-out film. It is indeed hardly possible to find 

 a sensitiser which acts upon all the dyes employed. Even 

 in the case of thiosinamine the employment of other 

 sensitisers is necessary to assist in obtaining regular 

 bleaching action. In 1908 I published the results of an 

 extended investigation into the sensitising effects of a 

 very large number of bodies (16). 



Attempts have been made to develop lightly printed 

 bleach-out prints by Kiimmel, Gebhardt, Limmer and 

 myself (17), and although certain results have been 

 obtained nothing of a practical nature has resulted from 

 the experiments. 



It is a pity that there are so few workers in this in- 

 teresting branch of science. Two of my most active 

 co-workers, Dr. Neuhauss and Dr. Gebhardt, have fallen a 

 prey to the war, and the few remaining ones belong, 

 unfortunately, all to enemy countries. 



I have brought a collection of thirty prints upon 

 " Utocolor" paper, mostly from Autochromes, to show the 

 nature of the results obtained. 



