228 SEC. 8. HEAT. 



Dry clay when exposed to high temperatures contracts uniformly, and 

 Wedgwood believed that by the amount of contraction the temperature 

 which produced it could be measured. The instrument, however, is not 

 reliable. This specimen was made by Josiah Wedgwood, and presented to 

 the Edinburgh Museum by his grandson Mr. Godfrey Wedgwood. 



1O71. Copper Pyrometer, for determining the temperature 

 of blasts. E. A. Cowper. 



The temperature of the blast is readily ascertained by heating a small 

 piece of copper in it, and then dropping the copper into a pint of water in a 

 copper vessel surrounded by a non-conductor, and where a thermometer 

 shows one degree for every fifty degrees the copper had been heated. The 

 thermometer is provided with two scales, one fixed, showing the temperature 

 of the water, the other sliding, showing the temperature of the blast. 



1074. Pyrometer. O. Schutte, Cologne. 



The pyrometer for determining the temperature of the heated blast-current 

 deserves particular attention on the part of proprietors, overseers, &c. of 

 foundries, on account of the simplicity of its construction, which is proof 

 against deranging influences, although constantly exposed to a destructive 

 element, viz., the glowing hot current, the more especially as no pyrometer 

 has been made as yet with which temperatures up to 600 degrees Celsius and 

 more can be continuously determined. 



By the application of this pyrometer it will be possible to control at any 

 time the apparatus and the stokers, and in cases where Siemens' or other 

 similar apparatus are employed, to determine the exact time when the same 

 must be reversed. The pyrometer, likewise, indicates any disturbing in- 

 fluences occurring in the flues, variations in the fuel, in the atmosphere, &c., 

 and thus offers the best guarantee that the heating of the apparatus is not 

 forced to such an extremity as to cause the destruction of the pipes, stop-valve, 

 &c. 



1074a. Water Pyrometer. C. W. Siemens. 



The pyrometer consists of a copper vessel, capable of holding rather more 

 than a pint of water, and well protected against radiation by having its sides 

 and bottom composed of a double casing, the inner compartment of which is 

 filled with felt. A good mercury thermometer is fixed in it, having, in addition 

 to the ordinary scale, a small sliding scale, graduated and figured with 50 

 degrees to 1 degree of the thermometer scale ; there are also some cylindrical 

 pieces of copper provided with the pyrometer, each accurately adjusted in 

 size, so that its total capacity for absorbing heat shall be l-50th that of a pint 

 of water. 



In using the pyrometer, a pint (0'56S litre, or 34'66 cubic inches) of water 

 is measured into the copper vessel, and the sliding pyrometer scale is set with 

 its zero at the temperature of the water as indicated by the mercury ther- 

 mometer ; a copper cylinder is then put into the furnace or hot blast current 

 the temperature of which it is wished to ascertain, and is allowed to become 

 heated for a time varying from 2 to 10 minutes, according to the intensity of 

 the heat to be measured. 



It is then to be withdrawn and quickly dropped into the water in the 

 copper vessel, where it raises the temperature of the water in the proportion 

 of 1 degree for each 50 degrees of the temperature of the copper. The rise 

 of the temperature may then be read off at once on the pyrometer scale, and, 

 if to this is added the temperature of the water as indicated on the mercury 

 thermometer before the experiment, the exact temperature required is 

 obtained 



