EYE-PRESERVING GLASS FOR SPECTACLES. 
17 
lime glass. The contents of a large potful of the melted flux was poured into cold 
water. The broken-up mass was sent to my laboratory and has been used in the 
preparation of the test glasses. The object of pouring the molten flux into water is to 
break it up and render it easy to powder for convenience of adding other ingredients. 
In this state I call it “ Fused Soda Flux.” 
Sometimes it is found advisable to use the flux in its raw state without previous 
melting, and when working upon the large scale this is the best plan. I then call it 
“ Raw Soda Flux.” 
Without counting numerous preliminary experiments, I have made and fully tested 
over 300 tinted glasses, the quantitative composition of each being known. From 
these glasses I have selected a certain number which possess valuable qualities in 
respect of athermancy, adiactinity, and transparency. 
I will now give the composition of these glasses, and the special properties in respect 
to the desired results. 
Glass 150. 
Fused soda flux. 90'00 
Cerium borate. 8'13 
Nickel sulphate, crystallised. 0'07 
Uranoso-uranic oxide. . 1'80 
lOO'OO 
In Glass 150 a small amount of nickel has been added to the cerium and uranium. 
The colour is pale yellow, and it is opaque to ultra-violet radiation, the limit being 
A 3613. It cuts oft* 37 per cent, of the heat radiation and transmits 73 per cent, of 
the incident light. The tintometer numbers are:—Red, 4'0 ; yellow, 3'5 ; blue, 0'5. 
Glass 158. 
Fused soda flux. 
Cerium borate. 
Ferroso-ferric oxide .... 
Chromic oxide ...... 
8975 
878 
2'03 
0'09 
lOO'OO 
This glass is pale greenish yellow. It is quite opaque to all the ultra-violet rays, 
the limit being A 3700. It cuts off 63 per cent, of heat radiation, and transmits 54 
per cent, of the light. 
The glass has a pale greenish yellow colour. Its tintometer numbers are :—Yellow, 
275 ; blue, 3'5. 
VOL. ccxiv.— A. 
D 
