486 
Romance  of  Chemical  Elements. 
(  Am.  Jour.  Pharm. 
<■       July,  1 918. 
rally  much  more  than  when  there  is  a  period  of  thirty-six  elements, 
as  in  the  case  of  the  period  in  which  the  rare  earth  metals  occur. 
In  the  periodic  system  they  form  a  group  from  cerium  to  lutecium, 
and  as  pointed  out  above,  their  difficult  separation  was  the  main 
cause  for  such  a  family  tree  as  Tables  IV  and  V  represent. 
Table  IV. 
The  Family  Tree  of  the  Cerit  Earths. 
Year. 
Disco\ 
1803 
1839 
1841 
1879 
1900 
1918 
Ceria 
Cerium  Lanthanum 
Number  58 
Symbol  Ce 
At.  weight  140 
Lanthanum  Didymium 
Didymium  Samarium 
Praseodymium 
Neodymium 
Samarium 
Europium 
1 
57 
La 
139 
59 
Pr 
141 
60 
Nd 
144 
61 
147 
62  63 
Sa  Eu 
150  152 
Berzelius 
Mosander 
Mosander 
Lecoq  de 
Boisfcaudran 
Auer  von 
Welsbach 
Demarcay 
The  platinum  metals  and  the  noble  gases  have  a  similar  history 
of  gradual  isolation,  as  Tables  VI  and  VII  show.  In  the  latter  the 
amounts  are  given  and  it  is  easy  to  understand  how  such  small  per- 
centages may  be  overlooked. 
History  of  Elements. 
In  history  the  chronological  method  of  tabulating  facts  has  many 
advantages,  and  I  have  followed  it  here  to  point  out  some  interesting 
things  connected  with  the  chemical  elements.  Beginning  with  ele- 
ments known  to  prehistoric  man  (but  naturally  not  as  elements),  we 
will  select  a  few  interesting  ones. 
Carbon. 
The  discovery  of  fire  was  the  greatest  step  toward  civilization 
and  anthropologists  tell  us  of  the  mighty  changes  which  the  cooking 
of  food  caused  in  the  human  features.  With  fire  primitive  man  be- 
came acquainted  with  carbon,  the  black  residue  of  incomplete  com- 
