SOIENCE AND INDUSTRY. 
all kinds, of range-finders, of light projection apparatus, signalling 
apparatus, and many other optical arrangements. (4) The great need 
of suitable sheet and plate glass for goggles and gas masks for airmen 
and soldiers, wind screens for aeroplanes and cars, plates for photo- 
graphic work, X-ray apparatus, glass tables for operations, and non- 
actinic and coloured glass of all kinds for special work. (5) The 
gnormous demand for ordinary glass bottles, jars, and food containers, 
not only for foods, but also for medical supplies and chemicals, &c. 
These are a few of the urgent demands on certain sections of the glass 
trade, which the general public may not have considered and which 
justified the industry being classed as a key industry, as the Govern- 
ment had to foster and support many of the factories, when converted to 
new purposes, and the industry-as a whole was placed under Govern- 
ment control. 
Let us -now look into the general conditions of the glass in- 
dustry and the developments during the war period. In the first 
place, the © majority of the British manufacturers had not kept 
pace with developments in the glass industry on the Continent. 
Many ‘had ideas that they possessed trade secrets, and they were opposed 
to any suggestions of scientific training for the workers or the alteration 
of their ‘methods, based on tradition and custom, to methods evolved by 
scientifid investigation. The furnaces in use were generally out of date, 
but were considered’ good enough for the purpose. They were, as a 
rule, circular coal-fired pot furnaces for the better class of glass, and 
were capable of heating 12 pots about 38 inches in diameter. Fach pot 
held about 15 ewt. of metal, so that 7 to 8 tons of glass were manu- 
factured in a week (only one batch was the custom), with a fuel con- 
sumption of 40 tons. The chief advance that had been made on this 
furnace was in the nature of the firmg. In the English furnace the 
leaking of a pot would result in the formation of great masses of clinker, 
clogging up the grate, reducing the general efficiency of the whole fur- 
nace, and often necessitating the digging out of the offending pot. In 
the new type, the coalwas first converted into gas. away from the glass 
furnace, which became much cleaner, and, on the Continent, was far 
better lighted. Although coal gas was first used, in America natural 
gas was also largely used, and these were replaced in Europe and 
America by producer gas, ’and. the air used for mixing for the com- 
bustion, was preheated by the waste heat from the furnace gases. 
~The. two best-known types are probably the Siemens regenerative 
and the Her mansen recuperative furnaces. 
‘Without going ‘into details, it will be sufficient to state that in the 
Siemens. regenerative . type the incoming air can be drawn in at either 
end alternately, passing through a heating chamber by a system of fire- 
_ brick channels, and is thus heated before mixing with the gaseous fuel. 
The direction ‘of the gases in combustion which play over the pots is 
reversed, by a system of flues, about every half-hour. ‘The waste gases, 
before. reaching the chimney, pass through either chamber ‘alternately 
at ‘the ends of the furnace, and thus supply heat, which is used to heat 
the incoming air.. When the batch is melted either regenerator may be 
-ettt out and straight draught and lower heat (no preheating of gases for 
combustion) may be used, until the batch is worked out. The main 
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