used as a Pyrometer in measuring High Temperatures. 539 



from which 



l+kx _ 760 P_-y\P_ 



1 + oar - V . 0-0012932 . 8 ' H IT 



M being a quantity which is constant for the same flask. 

 From which is obtained 



1-lig 



Mu^-k 



a = 0-00367. 



The method here described may be used in many cases, but it 

 requires that the introduction and removal of the apparatus from 

 the furnace takes place without detriment to the operation. I 

 have devised another apparatus, which has the advantage over 

 this of always remaining in one place, and of serving as often as 

 necessary to measure the variable temperatures of the same fur- 

 nace. I proposed to employ it in determining the temperatures 

 at which enamels and the different kinds of painting on porcelain 

 are baked at the Imperial Manufactory of Sevres. 



The apparatus consists of a tube, AB, fig. 7, of wrought 

 iron, the length of which varies according to the extent of the 

 space whose mean temperature is to be determined. Its internal 

 diameter varies from 2 to 5 centimetres ; it is more when the 

 tube is somewhat long. This tube is closed at both ends by 

 iron discs which are screwed and braced, each of which is pro- 

 vided with an iron capillary tube ab, cd passing through the 

 side E E' of the furnace. To construct these tubes, a very soft 

 and frequently reheated soft iron cylinder, perforated by a lon- 

 gitudinal aperture 3 or 4 millims. in diameter, is drawn out in 

 the drawing-frame. Each of these capillary tubes terminates 

 outside the furnace in a three-way stopcock, R R'. By means of 

 the stopcock R, the large tube A B can be successively connected 

 with either of the two tubulures e and/. By the stopcock 11' 

 the same tube communicates with either of the tubulures g, h. 

 The metallic tubulure h is soldered to the end of a copper tube 

 C, filled with oxide of copper. 



When the temperature of the furnaces is to be determined at 

 a given moment, the stopcocks R and R' are placed in the posi- 

 tions represented by fig. 7 ; by means of a caoutchouc tube, the 

 tubulure / is connected with an apparatus which furnishes a 

 constant supply of dried and purified hydrogen ; the hydrogen 

 expels the air of the tube A B through the tubulure g, which 

 remains open. The disengagement of hydrogen is continued 

 until the air is completely expelled: any oxide which might 



