Manchester Memoirs, Vol. Hi. (1908), No. 14- 



XIV. Some Observations on the Chemical Action of 

 Tropical Sunlight. 



By Gilbert John Fowler, D.Sc, F.I.C. 



Received and Read April 28th, igo8. 



In the early part of 1906 the author was called upon 

 to undertake certain investigations in connection with the 

 treatment of sewage, on behalf of the Government of 

 Bengal. The work was carried out for the most part in 

 Calcutta, and in the course of it, it became of importance 

 to determine the effect of tropical sunlight upon the 

 accuracy of iodine titrations, and upon the stability of 

 solutions of chloride of lime. 



Some quantitative record of the photo-chemical inten- 

 sity of the light was thus desirable. The most usual 

 method of photo-chemical measurement is by means of 

 standard silver chloride paper as originally suggested by 

 Bunsen and Roscoe.* Special paper is, however, required 

 to obtain satisfactory results by this method. 



Of the various forms of chemical actinometer, that 

 generally referred to as Eder's is fairly well known. Eder 

 determines under defined conditions the rate of reduction 

 of mercuric chloride to mercurous chloride by the action 

 of light in presence of ammonium oxalate. The sug- 

 gestion that this reaction could be used as a means of 

 measuring the photo-chemical intensity of light was first 

 made by the present writer's father, R. J. Fowler, in a 

 paper read before the British Association in Leeds in 

 i8s8.t 



* Po^g. Ann., vol. 124, 1865, p. 353. 

 t Report Brit. Assoc, Leeds, 1858, Chemistry, p. 47. 



June 4th, igo8. 



