560 NEW YORK: STATE MUSEUM 



Thermoelectric pyrometer. Le Claatelier's tliemio electric pyrome- 

 ter, depends on the measurement of a current generated by 

 the heating of a thermopile. The latter consists of two wires, one 

 of platinum and the other an alloy 90^ platinum and 10 fc rhodium, 

 twisted together at their free ends for a distance of about an inch, 

 while the next foot or two of their length is inclosed in a fire clay 

 tube, so that when the couple is inserted in the furnace only the 

 end which is held near the body whose temperature is to be meas- 

 ured will receive the full force of the heat. The two wires con- 

 nect with a galvanometer, the deflectibn of whose needle measures 

 the temperature at the point where the free end of the wire couple 

 is applied. As at present put on the market, the thermoelectric 

 pyrometer costs about $180, and the price, together with the deli- 

 cacy of the galvanometer, has tended to restrict its use. There is 

 no reason however why one should not be made and put on the 

 market for a much lower price. It is not necessary that the record- 

 ing instrument shall be in the immediate vicinity of the kiln; it 

 may be kept in another room where it is safe from dust and rough 

 handling, and the wires can extend from there to the kiln. This 

 pyrometer is considered to be accurate tO' within 10° F. 



Seger cones are very useful for determining the completion of 

 firing, but the thermoelectric pyrometer serves as a guide during 

 the burning operation, indicating whether the temperature is rising 

 slowly or quickly, and whether steadily or unevenly. 



If careful records are kept of these facts during the firing of a 

 kiln, and the results obtained compared, we are enabled to collect 

 valuable data concerning the conditions necessary. 



A crude means of judging temperature is to observe the color 

 of the fire as shown by the following table, which gives the color 

 of a body when heated to different degrees, thus: 



Just glowing in the dark ." 977° F. 



Dark red 1252° F. 



Cherry red ' 1666° F. 



Bright cherry red 1832° F. 



