2 
SIR WILLIAM CROOKES ON THE PREPARATION OF 
The area of the tank of molten glass is about 82 square yards, and it contains from 
300 to 350 tons of the mixture. There are several such tanks in the works. The 
tank is divided by a fireclay partition into two unequal parts. At the lower part is 
an opening through which the melted glass can flow. The larger portion of the tank, 
where the materials are melted together at a high heat, has a surface of about 
63 square yards. This is called the “ melting end ” ; when the mixture is well fused 
and homogeneous the molten glass flows through the opening into the c ‘ working 
end” of about 19 square yards, where the heat is less and the glass is in a viscous 
state. Fireclay rings of 18 inches internal diameter and a foot deep float on the 
surface of the viscid glass; any scum on the surface of the tank is thereby kept from 
contaminating the surface of the glass inside the ring. One ring floats opposite each 
working opening, and the workmen withdraw the requisite quantity of glass for each 
operation from the inner surface of the ring. 
The light from the melting end of the tank, viewed through a working opening, 
was brilliant white with a tinge of orange ; it was with difficulty the unprotected eye 
could make out any details. Viewed through dark glasses the surface of the metal in 
the tank appeared as a seething mass in constant commotion. The surface in the 
working end was more easy to see. It was of a bright yellow incandescence, and 
comparatively quiet. 
It is not certain what the temperatures are at each end of the tank. So far as one 
could judge, the temperature at the melting end is about 1500° O., and at the working 
end decidedly less—-say, 1200° C. 
About each opening, especially at the melting end, thin white vapours rose and 
settled on the surrounding cooler parts. A piece of paper held in this vapour 
instantly ignited. Examined with a hand spectroscope the yellow line of sodium was 
seen to be brilliant in this vapour, but the light from the molten glass showed a 
continuous spectrum in which the sodium line was visible. On one or two occasions a 
black line was seen in place of the yellow sodium line, showing a reversal. Some of 
the condensed vapour was collected from the cool sides of the working opening and 
chemically examined. It was found to consist principally of sodium and calcium 
sulphates, with a little sodium chloride. 
Photo- and Thermo-graphic Experiments. 
The spectrograph used for taking photographs of the radiation from the molten 
glass is the one I described in ‘Hoy. Soc. Proc.,’ vol. lxv., p. 237, May, 1899. It has 
two quartz prisms, each made up of two halves, one half being right- and the other 
half left-handed, according to Cornu’s plan for neutralising the effect of double 
refraction. The collimating and camera lenses and the double condensers are also of 
quartz cut in the same fashion. The slit jaws are made of two acute-angled quartz 
wedges, edge to edge. The refracting prisms are of 60 degrees angle, and each face 
