HYDROGEN INTO ATOMS 



183 



1. K should be independent of the pressure. 



2. K should vary with the temperature according to van't Hoff's equa- 

 tion ; that is, log K plotted against r/T should give a straight line. The 

 slope of this line determines the value of q. 



3. The value of q thus found should agree with that obtained at higher 

 pressures. 



We see by examination of the tables that the values of K, f ound«at the 

 three higher pressures 0.207, i.i and 4.4 mm. are in excellent agreement. 

 At 0.039 mm. the agreement is also good at the higher temperatures, but 

 poorer at the lower temperatures. The results at 0.015 mm. are consider- 

 ably lower than the others. On the whole, however, considering that these 

 experiments extend over a range of pressures of nearly 300-fold, the agree- 

 ment between the different values of K is surprisingly good. 



"JO 



3S 40 4S SO 



Fig. 2. — Experiments at low pressures. 



SS 



At the lowest pressures the correction for radiation from the filament is so 

 large that errors from this cause, particularly at the lower temperatures, 

 may perhaps account for the observed variation in K. 



In Fig. 3 the values of log K have been plotted against i/T. In order to 

 prevent the curves from overlapping, the successive curves have been dis- 

 placed vertically by one unit; thus log K is plotted for P = 0.015 mm., 

 while (i -f-log K) has been plotted for P = 0.039 and (2 -[-log K) for 

 P ^ 0.207, etc. The curves should be parallel and equidistant straight lines. 



