CHAPTER VII
THE MEASUREMENT OF HIGH TEMPERATURES IN GASWORKS
In the majority of gasworks duriag the past Century too much. dependence was placed upon the human eye and its ability to judge roughly between. the difference in temperature of heated objects. In the matter of retort benches and the like, the accuracy with which the trained individual can discern between correct and iacorrect working heats is remarkable ; but, to say the least of it, the method is crude and unworthy of the scientific procedure which is a feature of the modem gasmaking ■establishment. The pyrometer, accordingly, is now recognized as an instrument «ssential to the proper conduct of many of the everyday gasworks processes. Needless to say, the choice of a pyrometer depends essentially upon the purpose for which it is required. For instance, if it is to be employed in the laboratory or for research, work very much greater accuracy is needed than is the case with. the operations of the retort-house or water-gas plant, where an error of some 50° is of no great importance. In the latter case, therefore, it is usually advisable to sacrifice a certain amount of accuracy for portability and capability to withstand the somewhat trying conditions. In the matter of temperature recording appliances, the engineer has a large selection from which to choose, and it has been thought advisable to enumerate the various methods employed, followed by a brief description of the principle upon which. each. is operated.
Appliances for recording medium and high temperature may, in general, be ■classified as follows :—
(1) Prepared clay substances or alloys, e.g., Seger Cones, the Watkin Heat Hecorder, etc.
(2) Special Mercury Thermometers.
(3) Optical Pyrometers.
(4) Resistance Pyrometers.
(5) Expansion Pyrometers.
(6) Thermo-electric Pyrometers.
Reference is made to the use of Seger Cones in the chapter on Refractory Materials (see page 203). This metliod of determining temperature is, of course, necessarily only approximate, and while it forms a useful and handy nieans when •dealing with. such cases as refractories under test, it is scarcely applicable to the working processes assoeiated with gasworks. Temperature recorders of this kind 229