132 



CALORIFIC POWER OF FUELS. 



If the flue-gases be drawn off from the receiver B by 

 four tubes, CC, into a mixing-box, 

 D, beneath, a good mixture can be 

 obtained. Two such samplers, one 

 above the other, a foot apart, in the 

 same flue will furnish samples of 

 gases which show the same compo- 

 sition by analysis. 



The oil gas holder (Fig. 31) con- 

 sists of a bottle tubulated at the 

 bottom and connected with the sup- 

 ply of gas at the upper opening. It 

 may contain some 10 litres (600 

 cubic inches), and is filled with 

 water having on it a layer of 10 

 centimetres (4 inches) of oil. The 

 water running out from the tubu- 

 lature at the bottom draws the gas 

 in at the top. The stopper at the top has two openings, 

 through one of which passes a funnel-tube, through which 

 water may be poured to expel the gas when portions of it 

 are needed. The gas then passes out by the same tube 

 through which it was drawn into the bottle. 



With all kinds of aspirators or gas holders especial care 

 must be taken to prevent entrance of air into the flue after 

 leaving the fire, since the correct analysis will show not only 

 the quantity of unburnt gases, but also the excess of air, and 

 any mixture of outside air will vitiate the result and cause 

 faulty deductions as to the working of the fire ; and conse- 

 quently the waste calories. 



To prevent this, all joints in the masonry must be exam- 

 ined and repaired if necessary. In case of dampers, which 

 must be used, the bearings can be made in stuffing-boxes, as 

 recommended by Burnet. Generally, the gas can be sampled 

 before it arrives at a damper, as the course of the boiler-flue 



FIG. 31. OIL ASPIRATOR. 



