40 ATMOSPHERIC ACTINOMETRY 



One stpp fartlier might be taken. We have just ascei-tained that iu the solu- 

 tion of oxalic acid there takes place a kiud of storing "p of light, which shows 

 itself in an increase of sensitiveness as regards phenomena of oxidation. Might 

 not the oxygen which is present in the sohition, or even tliat w ]ii( Ii is constantly 

 dissolved there and transforaied, might it not itself he rendered sensitive, and so be 

 endowed w ith an oxidizing power -wliidi it cKidd afterwards use in diffused light i 



T have found nothing, while searching in this direction, with oxalic acid: tliis 

 reagent, f|uite sensitive enough for the study of powerful actions, is not sensitive 

 enough for such weak actions as that which I have just suggested. But 1 

 have been more successful with oxidizalde sul)stances of sharper reactions, so that 

 the veiy smallest vaiiations became measurable. This is the case with diastases ; 

 an almost infinitesimal quantity will jiroduce very apparent effects, and it is, there- 

 foi-e, easy to trace their disappearance by oxidation in the liquids which contained 

 them. AYith rennet especially the very smallest variations in (piantity can be aj»- 

 preciated from corresponding variations in tlie time of coagulation of equal quan- 

 tities of niilk, so that this diastase is very convenient for study. By siich means 

 I found that it oxidized and disappeared in water which had been previously 

 exposed to the sun, while it remained, if not quite intact, at least nearly so in the 

 same water as freshly drawn fr<)m the hydrant. I also ftnind that a glass flask 

 exposed to the sun stored up on its walls enough chemical radiations to accelerate 

 afterwards the oxidation of a solution of rennet, which was allowed to stand in the 

 shade. 



All these facts, upon which I do not insist because they go beyond the limits 

 of this work, enlarge the field of those phenomena to which they apply. If inso- 

 lated liquids and solids, may in certain cases, like our solutions of oxalic acid, 

 acquire properties which they had not before, the phenomena of solar combustion 

 may well extend below the surface, which has been directly illuminated, and assume 

 in the general economy of the world an importance, no doubt as yet inferior to 

 that of microscopic organisms, but certainly no longer to be neglected, as it has 

 been heietofore. 



Since I have entertained the views which I have developed in the preceding 

 pages, I liave investigated especially their agricultural and hygienic consequences. 



As far as hygiene is (•oucenieil, I have sliown niuiv clearly I think than 

 Messrs. Dowiies and Blunt that solar light kills the germs of microbes suspended 

 in the aii'. I have proved, moreover, that this destruction was preceded by a 

 veritable at(e/i nation.^ 



' Atina/es de Chimic ct dc Physique, 6th ser., vol. v., 1885. 



