] 64 Royal Institution. 



Great facility is afforded in the management of these furnaces. 

 If, whilst glass is in the course of manufacture, an intense heat is 

 required, an abundant supply of gas and air is given ; when the glass 

 is made, and the condition has to be reduced to working-tempera- 

 ture, the quantity of fuel and air is reduced. If the combustion in 

 the furnace is required to be gradual from end to end, the inlets of 

 air and gas are placed more or less apart the one from the other. 

 The gas is lighter than the air; and if a rapid evolution of heat is 

 required, as in a short puddling-furnace, the mouth of the gas inlet 

 is placed below that of the air inlet ; if the reverse is required, as in 

 the long tube- welding furnace, the contrary arrangement is used. 

 Sometimes, as in the enameller's furnace, which is a long muffle, it 

 is requisite that the heat be greater at the door end of the muffle 

 and furnace, because the goods, being put in and taken out at the 

 same end, those which enter last and are withdrawn first remain, 

 of course, for a shorter time in the heat at that end ; and though the 

 fuel and air enters first at one end and then at the other alternately, 

 still the necessary difference of temperature is preserved by the ad- 

 justment of the apertures at those ends. 



Not merely can the supply of gas and air to the furnace be 

 governed by valves in the passages, but the very manufacture of the 

 gas fuel itself can be diminished, or even stopped, by cutting off the 

 supply of air to the grate of the gas-producer ; and this is important, 

 inasmuch as there is no gasometer to receive and preserve the aeri- 

 form fuel, for it proceeds at once to the furnaces. 



Some of the furnaces have their contents open to the fuel and 

 combustion, as in the puddling and metal-melting arrangements ; 

 others are enclosed, as in the muffle furnaces and the flint-glass-fur- 

 naces. Because of the great cleanliness of the fuel, some of the 

 glass-furnaces, which before had closed pots, now have them open, 

 with great advantage to the working, and no detriment to the colour. 



The economy in the fuel is esteemed practically as one-half, even 

 when the same kind of coal is used either directly for the furnace or 

 for the gas-producer ; but as in the latter case the most worthless 

 kind can be employed, such as slack, &c, which can be converted 

 into a clean gaseous fuel at a distance from the place of the furnace, 

 so many advantages seem to present themselves in this part of the 

 arrangement. 



It will be seen that the system depends, in a great measure, upon 

 the intermediate production of carbonic oxide from coal, instead of 

 the direct production of carbonic acid. Now carbonic oxide is poi- 

 sonous, and, indeed, both these gases are very deleterious. Carbonic 

 acid must at last go into the atmosphere ; but the carbonic oxide 

 ceases to exist at the furnace, its time is short, and whilst existing 

 it is confined on its way from the gas-producer to the furnace, where 

 it becomes carbonic acid. No signs of harm from it have occurred, 

 although its application has been made in thirty furnaces or more. 



The following are some numbers that were used to convey general 

 impressions to the andience. Carbon, burnt perfectly into carbonic 

 acid in a gas-producer, would evolve about 4000° of heat, but if 

 burnt into carbonic oxide it would evolve only 1200°. The carbonic 



