EYE-PRESERVING GLASS FOR SPECTACLES. 
21 
Glass 246. 
This is a glass made on a larger scale at the Whitefriars Glass Works, and of the 
same composition to start with as Glass 240, namely, 10 per cent, of ferrous oxalate 
with raw soda flux. At the suggestion of Mr. Harry Powell a small quantity of red 
tartar and powdered wood charcoal was added to prevent oxidation; the resulting 
glass is sage-green in colour, a plate 2 mm. in thickness cuts off ultra-violet rays 
down to X 3800, its opacity to heat radiation is 98 per cent., and it transmits 27'6 of 
the incident light. The tintometer numbers are :—Yellow, 5'5 ; blue, 11‘0. 
A plate of this glass 1 mm. thick cuts off the ultra-violet rays down to X 3550, its 
opacity to heat radiation is 83 per cent., and it transmits 47‘9 per cent, of the incident 
light. The tintometer numbers are Yellow, 2‘25 ; blue, 5‘0. 
Glass 247. 
Raw soda flux . 
Cerium borate . 
Nickel oxide. 
Ferric oxide . 
Chromic oxide . 
100-00 
92-00 
6-30 
0-04 
P60 
0'06 
Glass 247 has a faint green tint and is practically opaque to the ultra-violet rays, 
the limit being X 3620. It obstructs 29 per cent, of the heat radiation, and transmits 
71 per cent, of the luminous rays. The tintometer numbers are :—-Yellow, 2"0 ; 
blue, 2*0. 
Glass 248. 
Fused soda flux ......... 94"60 
Cerium nitrate, crystallised. 4 "72 
Uranic oxide. 0"30 
Nickel oxide. 0"30 
Cobalt sulphate, crystallised. 0"08 
100-00 
Glass 248 is similar in composition to the one described in (197), p. 18, but is of 
a darker neutral tint. It is opaque to ultra-violet rays shorter than X 3550, and cuts 
off 47 per cent, of the heat radiation. It transmits 30 per cent, of the incident 
light. Its tintometer numbers are :—Red, 2"0 ; yellow, 2"5 ; blue, 7"5. 
