1880.] 



Actinism of the Sun's Rays and of Daylight. 



357 



49 c.c. of A with 1*0 c.c. of B ; colour after 40 minutes ; "1 Sunshine and 

 48-8 „ 1-2 „ „ 35 „ > cloud 



48"5 „ 1*5 ,, „ 30 ,, J alternately. 



48*5 „ 1*5 ,, in the diffused light of the laboratory ; 



no colour after 4 hours. 



Here we have action in sunlight in proportion to the acid. The 

 acid gives delicacy. The light commences the chemical action. 



Examples in which the decomposition was measured by a solution 

 of hyposulphite of sodium, which may be called solution C = 0'1 grm. 

 per litre of iodine (or as convenient). I shall extract experiments 

 made with B solution 0'8 cub. centim., because it is an intermediate 

 one (*2, *4, '8, 1*6, and 3'2 have hitherto been the favourites). 



1880. 





B sol. 





Measure by C solu- 

 tion (hyposulphite). 



Mar. 3 



Sunshine and cloud 



0-8 



After 



2J hours 



8*1. First colour 





alternately 









in 20' 



v 4 





0-8 







First colour in 30' 



„ 5 





0-8 



33 



4 „ 



0-9 



„ 8 



Sunshine 



0-8 



33 



21 „ 



7-5. Colour in 20' 



„ 9 



A little sunshine .... 



0-8 



5? 





4-8 



„ io 



Foggy, with a gleam 



08 



33 



Q 



1-5 





of sunshine 











» 11 



Bright 



0-8 





2i „ 



7-2 



» 12 





0-8 





3 „ 



0-6 



„ 13 





0-8 



5) 



21 „ 



Faint trace 



„ 15 





0-8 





"2 3) 



1-8 



„ 16 





0-8 



33 



2i „ 



1-6 



„ 18 



Sun through haze. . . . 



0-8 





21 „ 



5-8 



„ 19 





0-8 



33 



2* „ 



115 



„ 20 



Fog till 11.30 



0-8 



33 



2i „ 



32 



April 1 



Sun and showers .... 



0-8 





21 „ 



1-6 



Example of one day's observations showing the measured amounts 

 after 2| and 7 hours. C solution gives the proportion of light effect. 

 The light varied from hour to hour. 



B sol. 



0*2 c.c. 

 0-4 „ 



0- 8 „ 



1- 6 „ 

 3'2 „ 

 6-4 „ 



March 18th. Sunny. 

 C sol. required after 

 2i\ hours. 



1 



4 

 5 

 9 

 12 

 17 



25 c.c. 

 1 



The rate of increase of decomposit 



C sol. required after 

 7 hours. 

 5 -2 c.c. 



11 1 „ 



17-5 „ 



27 -0 „ 



33 -3 „ 



34 -8 „ 



on requires to be learned, also the 



most convenient solations of B for every light and perhaps temperature. 



