22 
SIR WILLIAM CROOKES ON THE PREPARATION OE 
Glass 249. 
Fused soda flux. 8 8'47 
Ferric oxide. 1'50 
Cobalt sulphate, crystallised. 0'03 
Cerium nitrate, crystallised. LO'OO 
lOO'OO 
Glass 249 is of a pale blue tint almost opaque to the ultra-violet rays, the limit of 
wave-length being A 3550 ; to all rays of shorter wave-length it is opaque. It cuts 
off 51 per cent, of the heat radiation, and transmits 63 per cent, of the luminous rays. 
Its tintometer numbers are :—Yellow, O' 5 ; blue, 2'0. 
Glass 250. 
Raw soda flux. 88'00 
Cerium borate.. 5'00 
Ferrous sulphate, crystallised . . . . 4'15 
Uranoso-uranic oxide. 2'75 
Chromic oxide. O'lO 
lOO'OO 
Glass 250 has a yellow colour with a faint tinge of green. It cuts off ultra-violet 
light, being opaque to radiation shorter than A 3685. It only obstructs 25 per cent, 
of the heat rays, and is transparent to the extent of 74 per cent. In the tintometer 
the numbers are :—Yellow, 7'00 ; blue, 1'25. 
** 
Glass 251. 
Raw soda flux. 92'0 
Ferrous sulphate, crystallised. 8'0 
lOO'O 
During the fusion the iron is partially peroxidised. Glass 25I ds of a faint yellow 
colour; it is opaque to ultra-violet rays shorter than A 3550, it obstructs 37 per cent, 
of the heat radiation, and it transmits 89 per cent, of the incident light. Its 
tintometer number is :—Yellow, 1'25. 
Glass 252. 
Raw soda flux. 72'60 
Cerium nitrate, crystallised. 24'90 
Copper sulphate, crystallised. 2'10 
Nickel oxide.• . . . 0'40 
lOO'OO 
