528 SCIENCE PROGRESS 



method cannot differ sensibly from those obtained by the 

 limiting density method, except in so far as errors are incurred 

 in effecting extrapolations. 



Leduc has arrived at the following atomic weights : 

 H = 1-0075, N = 14*006, C = 12-005, CI =35-45 (probably low). 



Comparison of Atomic Weights derived (i) by Chemical 

 Analysis and (ii) by Physical Methods 



The atomic weights deduced from the most trustworthy data 

 by the methods described in this article are as here tabulated : 



Table XII 



Density Critical Molecular 



Limits. Constants. Volumes. 



Hydrogen . . . 1-0076 1-0075 1-0075 



Nitrogen . . . 14008 14*010 14-006 



Carbon .... 12*009 12-003 12005 



Chlorine . . . 35-461 35'436 35'45 



The values for sulphur are unsatisfactory. The value for 

 phosphorus deduced by Guye's method is undoubtedly too 

 low and the same remark applies to Guye's value for chlorine. 

 These low values may possibly arise from a slight " association " 

 of hydrogen chloride and phosphine, the degree of association 

 varying between N. T. P. and the critical temperature and 

 pressure (22). Leduc (21) criticises his value for chlorine as 

 being, if anything, too low. 



The atomic weight of carbon obtained by these methods 

 approximates closely to the result obtained from the best gravi- 

 metric work. The rather high value obtained by Berthelot's 

 method suggests that the compressibilities of carbon monoxide 

 and methane need revision, a conclusion that may also be drawn 

 from an inspection of the compressibility measurements given 

 on p. 511. 



The atomic weight of hydrogen quoted above is in agreement 

 with the results of the best gravimetric work on the composition 

 of water but is distinctly an indication of the superior accuracy 

 of Morley's value (25) 1*0076 over that obtained subsequently by 

 Noyes (27), viz. 1*0078. Other considerations point to the same 

 conclusion. 



Special interest attaches to the atomic weight of nitrogen, to 

 which the physical methods assign a value slightly lower than 



