Hartley — On the Construction of Fume-Chambers. 357 



between April 10th and May 15th also give this quantity. As 

 the cubic contents of the chambers are 51-3 cubic feet, it means 

 that on an average the air of each chamber is completely changed 

 every nine seconds. It is important that the rate per minute, and 

 not the rate per hour, be stated ; because this indicates that the 

 exhaustion was practically continuous ; on the other hand, the 

 rate per hour might admit of intervals when there was no 

 exhaustion at all. 



The rate of flow of the heated gases within the flue being 

 influenced by so many different conditions, the majority of which 

 are not under control, and which may interfere with each other, 

 it was found useless to attempt to draw any conclusions by 

 plotting curves ; but it was, however, clearly shown that the 

 manner in which the gas is burnt is of importance, the ring- 

 burner being much the more economical, as it causes twice the 

 amount of exhaustion that is provided by the flaring- jet, for the 

 same volume of gas burnt. Notwithstanding this, it will be seen 

 that the flaring- jet is much the more efficient on the whole in 

 creating a draught. Lastly, I may draw attention to the small 

 height of the flues — about 25 feet — which have proved effective. 

 This renders such a means of ventilation readily adaptable to 

 small out-buildings, such as school laboratories, or to rooms at the 

 top of a building. Of course the longer the flues, the better the 

 exhaust. 



[Table. 



