206 Mr. W. Sutherland on the Spontaneous 



ordinate the points thus obtained ought, according to Bohr's 

 equations, to lie on two straight lines, and if in these equa- 

 tions k and k' are the same, both lines ought to pass through 

 the same point in the axis of pB : a glance at the points 

 when plotted shows that two straight lines passing through 

 such a point is the best representation for the second series 

 of experiments, and although Bohr's two equations for the 

 first series, representing two lines cutting the pB axis in two 

 distinct points, form a possible expression of the mean locus 

 of the points, still a representation which causes these points 

 to coincide is quite as good, the difference between the two 

 being less than the obvious errors of experiment. Thus for 

 Bohr's series I. we have the equations 



(p + a)B = k, (p + *')B = k, 



with a = *ll and a' = "043, while in series II. a = *10 and 

 a! =.'057 ; the value of k is not given because the mass of 

 the gas is unknown. It would appear as though a increased 

 with increasing temperature and a! decreased, while theo- 

 retically we should expect both a and a' to decrease, but the 

 temperature interval between the two series is too small to 

 allow of a safe inference as to the effect of temperature 

 on a. and a '. According to the theory the ratio of ct to a! is 

 that of the frequencies of encounters of 3 molecules with 

 one another before and after the region of discontinuity, and 

 from the above values it appears to be greater than 2 to 1 

 at 14° and less than 2 to 1 at 11°* 5, with very nearly a mean 

 value of 2 to 1 like the octave in music. Thus, when pure 

 3 is compressed, dissociation into 2 begins when N 2 /B 

 attains a certain value, and goes on in such a manner as to 

 keep N 2 /B constant till a point is reached at which, on further 

 reduction of volume, N 2 increases, but Nj decreases- in such 

 a manner as to keep (N 2 + N 1 )/B constant, so that although 

 volume diminishes pressure remains constant ; thus the pro- 

 cess of dissociation by encounters of the old periodicity 

 proportional to N 2 /B ceases and there is fresh combination 

 sufficient to keep (N 2 + N,)/B constant, but when by dimi- 

 nution of volume and combination N 2 /B has risen to double 

 its old constant value, dissociation begins again to occur on 

 further diminution of volume, as though the molecules of 3 

 w r ere now resonating to the octave of the old periodic collision 

 with a vigour that makes the presence of a great excess of 

 3 of little account ; this more rapid period is probably a 

 natural period of vibration of 3 , the other being an octave 

 lower. An interesting point about the discontinuity is the 

 similarity which it presents to the discontinuity of lique- 



