Glasses for protecting eyes from injurious radiations[3rd ed.] . blue-purple ultra, G 585 (D, 2= mm) green glass, Fig. 7, must be used instead of the cobalt blue, inorder to entirely eliminate the infra-red. As already mentioned, all the deep-blue glasses are quite opaqueto infra-red radiation, but none was found which is so effective inobstructing the infra-red as the bluish-green glass (Corning G 124JA) illustrated by E in Fig. 1. The latter, moreover, is verytransparent in the visible part of the spectrum. In that respectit compares favorably with Crookess darker shade of neutral glass
Glasses for protecting eyes from injurious radiations[3rd ed.] . blue-purple ultra, G 585 (D, 2= mm) green glass, Fig. 7, must be used instead of the cobalt blue, inorder to entirely eliminate the infra-red. As already mentioned, all the deep-blue glasses are quite opaqueto infra-red radiation, but none was found which is so effective inobstructing the infra-red as the bluish-green glass (Corning G 124JA) illustrated by E in Fig. 1. The latter, moreover, is verytransparent in the visible part of the spectrum. In that respectit compares favorably with Crookess darker shade of neutral glass 10 Technologic Papers of the Bureau of Standards (illustrated in Fig. 2), with the additional advantage of greateropacity in the infra-red. Some of these deep-blue glasses (e. g., Corning G 55; Schotts F3086) transmit 70 to 75 per cent in the blue and violet end of thespectrum, and hence are useful only in obstructing the infra-red rays. Purple Glass.—Curve A, Fig. 8, illustrates the transmission ofa deep purple glass (from the American Optical Co.; electric. /.0 SO ¥.0 Fig. 9 Amethyst glasses: B and C (*= and mm). A, colorless glass, Lab. No. 58, A. O. C. (t= .04 mm) smoke, purple), thickness mm. Curve B gives the trans-mission of an Arcweld goggle (thickness mm.), obtainedfrom a dealer. These two glasses evidently have the same com-position. This illustrates the desirability of adopting a definitetrade name for a particular kind of glass. The more opaque samples of electric-smoke glass are a deepred. However, the infra-red transmission is the same as for thepurple samples as shown in curve D, Fig. 3. Glasses for Protecting the Eyes 17 An interesting purple glass is Corning G 55A 62, which has anarrow transmission band in the violet and another narrow bandof high transmission at (See curve C, Fig. 8; mm.) A recent modification of this glass is Corning G glass, also Corning blue-purple ultra (G 585; curve D, Fig. 8),wi
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