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. _Pyrometers filled with Ether._-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. [Illustration: Fig. 4.--Mounting on horizontal pipes by thread on the tube.] [Illustration: Fig. 5.--Mounting by means of a clasp in reservoirs.] APPLICATION OF THE PYROMETER IN BONE BLACK FURNACES.