This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
The thermometers and pyrometers usually employed are almost all based on the expansion of some fluid or other, or upon that of different metals. The first can only be constructed with glass tubes, thus rendering them fragile. The second are often wanting in exactness, because of the change that the molecules of a solid body undergo through heat, thus preventing them from returning to exactly their first position on cooling.
Fig. 1.--Pyrometer with Electric Indicator.
The principle of the Seyfferth pyrometer is based on the fact that the pressure of saturated vapors, that is, vapors which remain in communication with the liquid which has produced them, preserves a constant ratio with the temperature of such liquid, while, on the other hand, the temperature of the latter when shut up in a vessel will correspond exactly with that of the medium into which it is introduced.
Fig. 2.--Method of Mounting by means of a
cone on vacuum apparatus.
Fig. 3.--Mounting by means of a sleeve on vacuum apparatus.
This instrument is composed of a metallic vessel or tube which contains the liquid to be exposed to heat, and of a spring manometric apparatus communicating with the tube, and by means of which the existing temperature is shown. The dial may be provided with index needles to show minimum and maximum temperatures, as well as be connected with electric bells (Fig. 1) giving one or more signals at maximum and minimum temperatures. The vessel to contain the liquid may be of any form whatever, but it is usually made in the shape of a straight or a bent tube. The nature of the metal of which the latter is made is subordinate, not only to the maximum temperature to which the apparatus are to be exposed, but also to the nature of the liquid employed. It is of either yellow metal or iron. To prevent oxidation of the tube, when iron is employed, it is inclosed within another iron tube and the space between the two is filled in with lead. When the apparatus is exposed to a high temperature the lead melts and prevents the air from reaching the inner tube, so that no oxidation can take place.
These are tubular, and constructed of yellow metal, and are graduated from 35° C. to 120°. They are used for obtaining temperatures in vacuum apparatus, cooking apparatus, diffusion apparatus, saturators, etc. Figs. 2, 3, 4, and 5, show the different modes of mounting the apparatus according to the purpose for which it is designed.
Pyrometers filled with distilled water are used for ascertaining temperatures ranging from 100° to 265° C., 80° to 210° R., or 212° to 510° F.
Pyrometers filled with mercury are constructed for ascertaining temperatures from 360° to 750° C.
Fig. 4.--Mounting on horizontal pipes by
thread on the tube.
Fig. 5.--Mounting by means of a clasp