140 A. Pedler — Bleaching action of light on colouring matters. [No. 2, 



which the colours are destroyed is unknown. The action of light upon 

 sensitive organic substances has been little investigated generally, but 

 a number of single observations of an interesting nature have been 

 lately made on this subject," etc. Hence it would appear there is still 

 room for further experimentation on this subject. 



The bleaching effect of sunlight or diffused light on colours or 

 coloured fabrics, may be due to several causes. These causes may, per- 

 haps, be summarized as follows : — 



1. The bleaching may be due to a decomposing action of the 

 light itself, unaided by any chemical action of the oxygen, carbon dioxide, 

 moisture, ozone, etc., present in the air, or even, though not at all pro- 

 bable in the great majority of cases, the loss of colour may be due to the 

 colouring matter itself being volatile. 



2. The bleaching may be caused by the light inducing some 

 chemical action due to the oxygen, carbon dioxide, moisture, ozone, etc., 

 of the air. 



3. Or in the case of dyed colours, the bleaching may be due to 

 some action between the organic matters of the fabrics, and the 

 colouring matters under the influence of light, or to a similar action 

 accompanied by a chemical action due to the oxygen, carbon dioxide, 

 moisture, etc., contained in the air. 



4. Also the bleaching action may be due to changes connected 

 with the growth of certain low forms of life, such as germinate when 

 bodies in a favourable condition are freely exposed to ordinary air, in 

 which such germs of life practically always exist. 



To test these propositions early in 1891, the following sets of 

 experiments were started. 



A series of six colouring matters representing roughly different 

 parts of a spectrum was taken. The colours were Purple as represent- 

 ed by neutral Litmus, Blue by Methyl Blue, Green by Methyl Green, 

 Orange by Methyl Orange, Pink by Eosine, and Red by Rosaniline 

 Acetate. Solutions of these substances were taken of definite strength 

 (4 grams in a litre of water), so that they could be always reproduced 

 when required. With these solutions specimens of pure cotton-wool as 

 representing organic matter such as used in various dyed fabrics, and 

 asbestus, representing an inorganic surface, which would have no practi- 

 cal chemical action on colouring matters, were dyed, and afterwards 

 carefully dried. With these three sets of materials, i.e., the solutions, 

 the dyed cotton, and the dyed asbestus, the following principal sets of 

 experiments were made : — 



A. The solutions were placed in tubes stoppered merely with 

 cotton-wool, and were then exposed freely to the action of the air and 



