Hartley — On the Construction of Fume-Chambers. 353 



Into this is fitted a gas-delivery tube which projects about 3 in. 

 into the interior. It is connected on the outside with the gas- 

 supply by means of flexible tubing ; and on the inside it is con- 

 nected in a similar manner with a large ring-burner of Fletcher's 

 make (about 9 in. diameter), supported on a ledge of brickwork 

 which on the right-hand side is 5 in. wide, and on the frontal 

 wall of the flue is 6 in. wide. In some cases the ring-burner is 

 dispensed with, and the flue is warmed by a flaring gas-flame 

 burning from the end of the tube which is screwed into the door. 

 It should be remarked, however, that the ring-burner is twice as 

 effective as the flaring gas-flame for the same quantity of gas 

 burnt. The entrance to the flue being horizontal, no drip or dirt 

 can drop into the vessels standing in the chamber ; moreover, as 

 it is about 12 inches above the floor, it is at the height which 

 experience has shown that in the majority of operations the 

 noxious fumes and gases are evolved. They do not rise through 

 the air of the chamber, but pass directly into the flue, along with 

 the supply of air which is necessary for the combustion of the 

 gas. This latter quantity is very large, and as the velocity of the 

 upward current of heated air and the products of combustion is 

 very great, owing to the flue being vertical, and freely discharging 

 vertically into the open air, there is nothing deposited on the walls 

 of the flue, nor upon the ring-burner, which therefore remains 

 quite free from moisture or acid, and consequently from corrosion. 

 In fact, the ring-burner is not corroded by such substances as 

 oil of vitriol and hydrofluoric acid evaporated in large quantities. 

 Above all considerations, we have the security of the upward 

 current being constant under all conditions. On no occasion has 

 any interruption of the draught or any downward current been 

 observed, even in the most tempestuous weather. The air from 

 every possible inlet, whether above or below, travels through the 

 chamber directly to the entrance to the flue. So strong is the 

 draught that when the sash is raised only an inch or two a Bunsen 

 flame is made to bend over horizontally ; and it is best to work 

 with the sash raised for at least a foot. 



Should any inflammable liquid within the chamber take fire, 

 the flames roar up the flue without causing any damage, since it 

 is built of fire-brick. Each of the three fume-chambers has a 

 cubic capacity of 51'30 cubic feet ; and the rate of extraction is, 



2F2 



