EXPERIMENTS ON KAOLIXIZATION. 



295 



They passed out of the boiler through tubulures (also omitted in the figure) 

 placed conveniently on its sides, the hose and wire being secured by small 

 perforated corks. Of course no attention was paid to the purity of the 

 metal employed. The silver and bismuth were fastened together by melting 

 a little globule on the end of the silver wire, and then applying it, while 

 still hot, to the end of a bismuth bar. The soldering thus produced was 

 very perfect. The platinum and bisnmth had, however, to be soldered 

 together by ordinary means. 



Method of measurement. — The relatlou bctwccn tlie clcctromoti ve force e, due 

 to the temperatures T and / (T^t) of the ends of the thermo-element, can 

 be expressed with the aid of two constants, a and h, thus: 



e = (T-t) [a + h(T+t)l 



But as T — t in this case is a very small (juantity (a few hundredths of 

 a degree), 



where T is the temperature of ebullition of the water as given by the aid of 

 the barometer. Knowing, there- 

 fore, o, h, and the barometric 

 height we are able to find Jt, 

 or the difi"erence of temperature 

 between the interior and the 

 exterior of the rock chamber (x 

 and z in Fig. 1 9). 



For the measurement of c 

 a "zero" method was employed. 

 In Fig. 20 a diagram of the con- 

 nections as actually made is 

 given, for the purpose of calling 

 attention to a few details of im- 

 portance in measurements of I'ig. 20.— Disposition of apparatus. 



this kind. The ])latinum terminals of the thermo-element e are soldered to 

 copper circuit wires at 1', the points of junction being immersed in a reservoir 



