A Manometric Actinometer for the Visible Spectrum 79 



If, for example, the vessel is shaken in light whose intensity and spectral distribu- 

 tion change with time, then one single manometric reading taken at the end of a 

 given period gives the number of quanta which have entered the vessel during the 

 whole period. 



There is one limitation of the instrument : i.e., that the light entering the vessel 

 must be completely absorbed. Under the conditions given above, the instrument 

 can be used from 670 mit in the red to the blue end of the visible spectrum. How 

 far it can be used in the ultraviolet must still be investigated. Quartz vessels must 

 be used instead of glass vessels. 



Direct Photooxidation of Thiourea 



Two hundred mg of thiourea, dissolved in 5 cc. pyridine, were introduced into the 

 rectangular glass vessel and illuminated — without addition of Chlorophyll or por- 

 phyrin — by a 100 w. mercury vapor lamp in a "black glass" envelope, at about 15 

 cm. distance. In 45 min., 24 mm. 3 0> were taken up. 



Summary 



A chemical actinometer has been described, by which quantum intensities in the 

 greater part of the visible spectrum can be measured manometrically. 



References 



1 Tappeiner, H. v., Ergeb. Physiol. 8 (1909), 698. 4 Gaffron, H., Chem. Ber. 60 (1.927), 755. 



2 Sheppard, S. E., Phot. J. 65 (1925), 380. 5 Warburg, O., and Negelein, E., Chem. Ber. 63(1930), 

 3a Warburg, O., Biochem. Z. 100 (1919), 230. 1816 . lemberg, R., Biochem. J. 29 (1935), 1322; 

 3b Warburg, O., and Negelein, E., Z. physik. Chem. Stier, E., Z. phvsiol. Chem. 275 (1942), 155. 



102 (1922), 236; 106 (1923), 191. 



