130
MODERN GASWORKS PRACTICE
the indicator points to between 30 and 60. Some engineers prefer to employ a recording gauge, so that a continuous record is taken.
ANALYSIS OF FURNACE GASES AND WASTE GASES
When drawing off samples of gas from different positions in a regenerator setting, care should be taken that the sample is a true and representative one, and the tester should feel asstired that there is nothing faulty in the method employed or m the apparatus he may be using. For drawing off a sample of waste gas enter-
Fig. 67.—The Wkight-Orsat Appaeatus.
mg the regenerative portion of a retort setting, it is necessary to consider the temperature which th.e sampling tube has to with-stand. Anything from 700°-l,000° C. may be experienced, and nothing short of porcelain, silica, or a water-cooled iron tube will answer the purpose. Uncooled metal tubes are out of the question by reason of their tendency to convert carbon monoxide into carbon dioxide even at a duli red heat. It has been stated that the composition of a gaseous mixture may be changed from 1-5 to 26-0 per cent. CO2 by the passage through an iron tube heated to a dull red heat, the carbon monoxide originally present reHncing the iron oxide with. the formation of carbon dioxide.
With careful handling a porcelain tube will answer the purpose very well. The tube should not be less than. 36 inches in length, and should have a diameter of at least f-inch. To preserve the tube against damage it should be wrapped round with asbestos string before being inserted into the -flue ; and, further, a fireclay tapered brick should be prepared of such, dimensions as will allow of its entry, wedge fashion, into the sight-box of the waste-gas flue to be tested—the taper brick having a hole in it sufficiently large to receive the asbestos-jacketed porcelain tube.
The joint should be made secure by means of fireclay. The apparatus which is best adapted for the analysis of furnace gas is the modified Orsat as shown in Fig. 67. It is portable, not easily damaged, and is simple to manipulate. It is sufficiently accurate for all technical purposes’ and always ready for use.