148 CALORIFIC POWER OF FUELS. 



increase of pressure and a lowering of temperature which 

 would diminish the density of the air one half. A corres- 

 ponding quantity of mercury passes into the arm of the tube, 

 and the original compensating weight is diminished by that 

 amount. A graduated index shows the variations of weight, 

 and hence the variations of density in the gases. An inge- 

 nious arrangement allows regulation by rotating the U-tube 

 on the axis pn. The tube is turned slowly around till 

 adjusted, thus changing the length of the lever-arm. 



A difference of I per cent of carbonic acid causes a differ- 

 ence in weight of 20 milligrams. One litre of air at o and 

 760 millimetres weighs 1294 milligrams; I litre of carbonic 

 acid weighs 1967 milligrams; the difference is 673 milligrams. 

 If the gas contains I per cent of CO 2 , each litre increases 6.73 

 milligrams in weight; and as the balloon contains 3 litres, it 

 supports an external pressure of more than 3 X 6.73 = 20.19 

 milligrams (0.311 grains). 



To prevent action of sulphurous acid the bearings are 

 made of sapphire, onyx, bloodstone, etc., and metallic parts of 

 phosphor-bronze. 



To set up the dasymeter, connect pipe e with the boiler- 

 flue before the damper; the tube pleads to the chimney. By 

 this means a current of gas passes through the box, and shows 

 at any time the percentage of carbonic acid. Siegert gives 

 the following results obtained with it, and the corresponding 

 results by analysis : 



j Dasymeter, 13.0, 13.0, 12.0, 6.25, 2.2, 16.3, 7.5, 12.5 

 3 ( Analysis, 13.0, 12.7, 12.2,6.00,2.0, 16.0,8.0, 13.0 



ECONOMETER. 



H. Arndt has invented what he calls the " Econometer " 

 (Fig. 37), which is on a similar principle.* It consists of a 

 tight cast-iron shell, NN, containing a gas-balance. A pipe, 



* Zeitschrift des Vereines Deutscher Ingenieure, xxxvu. p. 801. 



