COLORED GLASSES. 



55 



Blue-violet Glass. 

 (Schott's 1 No. F 3086; ^ = 2.58 mm.) 



In fig. 38 is given the transmission of a plate of blue-violet glass. There 

 is a large absorption band at 0.5 to 2 //, followed by smaller bands at 2.1 

 and 3.5 /i. In the deep infra-red such a band would cause selective re- 

 flection. In the present case the absorption band is due to the metal 

 behaving somewhat like an optically turbid medium. Using a pocket 

 spectroscope close to a Nernst glower, it was found that a trace of yellow 



Fig. 38. Blue-violet glass. 



at 0.56 n and of red at 0.707 /x was transmitted, the intensity of the maxima 

 being of the order of 0.01 per cent. In the violet the transmission was 

 30 per cent. This region was studied with a spectrophotometer. Ang- 

 strom has very ingeniously applied this glass in measuring the violet radia- 

 tion from the sun; using an absorption cell of water, 1 cm. thick, in addition 

 to this glass plate, all the radiation beyond 0.5 is absorbed. 



Green Glass. 

 (Schott's copper oxide, No. 431 III. Fig. 39. Thickness ^ = 3.43 mm -) 



The specimen examined showed an absorption band in the violet and 

 a second one in the red. There appears to be a small band at 2 /*, beyond 

 which point there is the usual absorption of uncolored glass. The band 

 at 2.95 p, found in silicates, e.g., mica, seems to be intensified by the pres- 

 ence of coloring substance, while the transmission seems to be terminated 

 at a shorter wave-length (also due to the coloring substance) than would 

 be found in a clear plate of glass of the same thickness. 



Ruby Glass. 



(Fig. 40. Curve a, Schott's monochromatic red, No. 2745; ^=3.18 mm. 



Curve b, impure red; / = 2.48 mm.) 



The monochromatic red glass examined is used in the Holborn and 

 Kurlbaum pyrometer. The second sample, curve b, transmitted impure 



1 See Zsigmondy, Zs. fur Instrk., 21, p. 97, 1901. 



