ATOMIC WEIGHTS 63 



That iSj the atomic weight of chlorine, when H=l, is 35.1911. If 

 = 16, then CI = 35.4652, ±.0005. 



For the weight of a normal litre of hydrochloric acid, G-uye and Ter 

 Gazarian ^ give the subjoined figures : 



1.6404 

 1.6397 

 1.6389 

 1.6401 



Mean, 1.0398, ± .00007 



Eeducing these by the method of critical constants, in which the term 

 (l + ^o) (l-6o) =1-00773, the molecular weight of HCl becomes 36.4693, 

 ±.0015. Hence, if H = 1.0078, Cl = 35.4615, ±.0015. 



In a preliminary note Gray and Burt ^ have given the results of their 

 investigation upon the density and composition by volume of hydro- 

 chloric acid. For the weight of the normal litre of the gas, as a mean of 

 twenty experiments, the value 1.63885 grammes was found, ±.00004. 

 By passage over heated aluminum the volume of hydrogen liberated from 

 two volumes of HCl was found to be 1. 00790, ±. 00002 ; the mean of 

 eight experiments. From these data, with H = 1.0078, and with Morley's 

 value and probable error for the density of hydrogen, HCl = 36.4672, 

 ±.0009, and CI = 35.4594, ±.0009. 



The several values for CI now combine thus: 



By syntheses of HCl 35.4652, ± .0005 



From density of HCl 35.4615, ± .0015 



From volumetric composition of HCl. . 35.4594, ± .0009 



General mean 35.4637, ± .00042 



This value is still to be modified by the analyses of nitrosjd chloride, 

 as given in the next section of this work. 



Addenda. Since the foregoing pages on the chlorine-hydrogen ratio 

 were written, and after the final mean had been utilized in a large num- 

 ber of other calculations, the complete work of Gray and Burt^ has 

 appeared. First, three series of determinations of the density of HCl 

 are given, with the weight of one litre of the gas at 0°, 760 mm., and at 

 London, as follows : 



1 Compt. Rend., 143. 1233. 1906. 



^ Proc. Chem. Soc. , 24, 215. 1908. For changes and corrections see addenda to this section. 



^Journ. Chem. Soc, 95, 1633. 1909. 



