380 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



and that the oxygen in the acid is five times 1 that in the 

 base (Berzelius, Chemical Proportions , 1819, p. 124). 

 The proportions of the three elements are : 



Lead Nitrogen Oxygen 



LEAD NITRATE = 62*3 7 : 8*52 : 29*11 grams 



62*37 8'ij2 2Q - II 



: : atoms 



207*1 14*01 16 



= 0*301 : 0*608 : 1*819 atoms 

 = i : 2 : 6 atoms 



Formula PbN 2 O 6 . 



SUMMARY AND SUPPLEMENT 

 A. VAPOUR-DENSITIES 



Vapour-densities have been determined for the following 

 metals and metallic compounds : 



Elements : Na, K, Zn, Cd, Hg. 



Haloid Salts: KI, Cu 2 Cl 2 , AgCl, ZnCl 2 , PbCl 2 , 2A1C1 3 Z 

 Al 2 Cl fl , Al 2 Br r> , A1 2 I C , 2FeCl2^Fe 2 Cl 4 , Fe 2 Cl 6 ^2FeCl 3 ^ 

 2FeCl 2 + Cl 2 , CrO 2 Cl 2 , CrCl 3 , MnCl 2 , SnCl 2 =^Sn 2 Cl 4 , SnCl 4 , 

 HgCl 2 , Hg 2 Cl 2 ^Hg + HgCl 2 , etc., in addition to com- 

 pounds of As, Sb, Bi. 



Carbon Compounds: Zn(CH 3 ) 2 , Zn(C 2 H 5 ) 2 , Zn(C 5 H n ) 2 , 

 A1(CII 3 ) 3 , A1(C 2 H 5 ) 3 , Sn(CH 3 ) 4 , Sn,(C 2 H 6 ) c , Fe(CO) 6 , 

 Ni(CO) 5 . 



The data are too scanty to give trustworthy values for the 

 atomic weights of the metals. 



B. ATOMIC HEATS 



The chief method for determining the atomic weights of the 

 metals is by means of the Law of Dulong and Petit (1819), 



specific heat x atomic weight = atomic heat = constant. 

 The value of the "constant" is about 6 for the range from 100 



1 In 1812 Berzelius regarded nitrogen as an oxide, and concluded 

 that this ratio was six times ; in 1819 he gave the ratio as six times or 

 five times, according as nitrogen was regarded as a compound or as an 

 element. 



