This instrument, shown in Fig. 204, continuously indicates the relative degree of cleanliness of the blast-furnace gas going to the gas engines, and is extensively used in European gas-engine stations. Gas from the cleaned gas main passes through this apparatus and impings upon a continuous recording chart, upon which the dust and the gas is deposited. The variations in the amount of dust in the gas are indicated by lighter or darker shades on the recording paper, depending on the amount of dust deposited. The flow of gas to the instrument is maintained either by the natural pressure of the gas, or, if this is not sufficient, by an aspirator behind the outlet pipe. The speed of the gas to the nozzle is kept constant by means of a regulator, as shown in sketch, the excess gas over the required amount escaping into the outlet pipe by passing under a partition and through a seal of water.

The Kapnograph.

Fig. 204. The Kapnograph.

Methods Of Determining The Amount Of Dust In Blast-Furnace Gas

A method employed with good results in Europe for determining the amount of dust in the gas consists in drawing a definite quantity of the blast-furnace gas to be tested through a filter, which is weighed in a dry condition before and after the test. The apparatus for determining the amount of dust consists of a glass tube drawn out at one end and fitted at the other with a ground-glass cover which is also drawn out to a thin tube. This cover facilitates the placing of the filtering material in the tube, and during the test the cover is fastened to the tube by means of wire. Before the test, the glass tube, filled with suitable filtering material, is placed in a drying furnace and heated at a temperature of 105° C. until its weight is constant, which usually requires from one to two hours. The drying furnace is arranged so that several tubes can be dried simultaneously.

"During the drying process air is drawn through the tubes after having previously been thoroughly dried by passing through bottles containing calcium chloride and concentrated sulphuric acid. During the drying process the tubes are weighed until no further decrease in weight is observed.

"In making the test, the weighed tube containing its filtering material is inserted into the gas main, a rubber stopper keeping the test-hole tight. The upper end of the tube is connected with a gas meter, which in turn is connected with a barrel filled with water. The water is allowed to flow out of the barrel and in so doing creates the necessary suction to draw the gas through the filtering tube and through the gas meter. When the necessary amount of gas has been withdrawn the tube is again dried and weighed. The increase in weight indicates the amount of dust in the quantity of gas tested.