Am.  Jour.  Pharm.  ) 
January,  1920. j 
Report  on  Atomic  Weights. 
33 
Na2B407,  and  their  chief  difficulty  was  in  insuring  the  complete 
dehydration  of  that  compound.  The  salt  was  then  converted,  in  a 
series  of  successive  experiments,  into  sodium  sulphate,  carbonate, 
nitrate,  chloride  and  fluoride,  which  gave  8  independent  values  for 
boron  ranging  from  10.896  to  10.905,  in  mean,  10.900.  This  value 
was  computed  with  Na  =  22.997,  ^  =  35457»  ^  =  32.064,  N  = 
14.010  and  C  =  12.005.  The  authors  finally  discuss  all  previous 
determinations  and  show  wherein  they  were  affected  by  errors. 
The  new  value  10.900  should  be  adopted  as  the  most  probable. 
In  this  research  sodium  fluoride  was  compared  not  only  with 
borax  but  also  with  the  sulphate,  and  the  8  values  found  ranged  from 
19.002  to  19.008,  in  mean  19.005.  The  rounded-off  value  F  =  19.0 
may  be  retained  for  all  practical  purposes. 
Lkad. — Oechsner  de  Coninck  and  Gerard^ ^  have  attempted  to 
determine  the  atomic  weight  of  lead  by  calcination  of  the  nitrate, 
and  find  Pb  =  206.98  when  N2O5  =  108.  This  determination  is 
evidently  of  no  present  value.  With  this  exception  the  other  recent 
researches  relative  to  this  constant  have  referred  to  isotopic  lead, 
and  the  normal  element  is  considered  only  in  comparison  with  it. 
Richards  and  Wadsworth,^^  for  instance,  find  for  normal  lead  Pb  = 
107.183,  and  Richards  and  HalP^  give  Pb  =  207.187,  values  slightly 
lower  than  the  accepted  207.20  as  determined  by  Baxter  and  Grover. 
Similar  determinations  by  A.  L.  Davis^^  gave  discordant  results. 
As  for  isotopic  lead  its  atomic  weight  is  so  variable  as  to  show  that 
it  is  nearly,  if  not  always,  a  mixture  of  isotopes,  and  not  a  constant 
which  can  as  yet  be  placed  in  the  table.  The  values  found  have  very 
great  significance,  but  they  are  far  from  final. 
GaIvIvIUM. — By  the  analysis  of  carefully  purified  gallium  chloride, 
Richards,  Craig  and  Sameshima^^  find  Ga  =  70.09  and  70.11.  These 
determinations,  however,  are  only  preliminary,  but  they  justify  the 
provisional  adoption  of  the  value  70.10.    The  original  values  given 
11  Compt.  rend.,  163:  415,  1916. 
^2  /.  Am.  Chem.  Soc,  38:  2613,  1916. 
13  Ihid.,  39:  537,  1917. 
/.  Phys.  Chem.,  22:  631,  1918. 
For  discussions  regarding  the  atomic  weight  of  isotopic  lead  see  the  Presi- 
dential address  of  Richards  before  the  American  Association  for  the  Advance- 
ment of  Science,  in  December,  1918.  Also  F.  W.  Clarke,  Proc.  Nat.  Acad.  Sci., 
4:  181,  1918. 
"  Proc.  Nat.  Acad.  Sci.,  4:  387,  1918. 
