PRESSURE COEFFICIENT OF RESISTANCE. 159 



other; its melting point appeared to be sharper and its yellow color 

 not so pronounced. These samples were transferred to capillaries of 

 thin glass provided with four platinum terminals sealed through the 

 glass, two for current and two for potential leads. The measurements 

 were made in the regular way on the potentipmeter. The details of 

 the method of transferring to the capillary need not be described; it is 

 possible to improve it. 



Measurements were made on the first and purer sample with a view 

 to establishing the temperature coefficient over the range to 12000 kg. 

 In order to avoid melting at atmospheric pressure, the temperature 

 range of the measurements was low, from 0° to 16°. Over this range 

 of pressure and temperature the most puzzling results were found. 

 At low pressures the resistance apparently decreased greatly with 

 increasing pressure, which was the result expected, but at higher 

 pressures the resistance increased again. After a day's run, the 

 apparatus was taken apart in the search for trouble, and the glass 

 capillary was found cracked, so that air got at the caesium and de- 

 stroyed it. The crack in the capillary had no effect on the measure- 

 ments, however. The temperature coefficient of this first and purer 

 sample between 0° and 16° was found to be 0.0054, which is high, and 

 evidence of good purity. 



The second sample, as already stated, seemed to be less pure initially, 

 and during the manipulation received further impurity because of the 

 accidental access of a small quantity of air to the inside of the appa- 

 ratus during the transfer to the capillary. This heightened the yellow 

 color and dirtied the metal so that it left a yellow scum on the glass, 

 whereas the first sample had run as cleanly through the glass as clean 

 mercury. However, the impurities introduced in this way were 

 obviously non-metallic, and there is no reason to expect that this 

 impurity introduced any essential change in the phase relations of the 

 different polymorphic forms. 



With the information received from the first sample it was possible 

 to direct the measurements on the second sample much more intelli- 

 gently, and to definitely establish the more important features. In 

 the first place it was established that caesium has a new modification 

 at high pressures, that the transition point is sharp, as it should be for 

 a true transition, and that the transition pressure varies with the 

 temperature. Two measurements were made of the transition pres- 

 sure at 0°. The first of these established that the equilibrium point 

 was contained between two pressure limits 140 kg. apart, and that the 

 mean point was 1960 kg. The second measurement shut the transi- 



