228       Recent  Literature  Relating  to  Pharmacy.    { ^m  May'/wX?™* 
From  this  very  small  quantity  of  pure  radium,  the  atomic  weight 
was  determined  by  weighing  the  amount  of  chlorine  present  in  a  given 
amount  of  radium  chloride,  as  silver  chloride.  From  a  number  of 
experiments  the  average  was  found  to  indicate  an  atomic  weight  of 
225.  Barium  chloride  under  similar  conditions  indicates  an  atomic 
weight  between  137  and  138. 
An  interesting  observation  was  made  in  this  connection;  it  was 
found  that  the  precipitated  silver  chloride  invariably  had  radioactive 
properties  without  containing  any  appreciable  quantities  of  radium. 
This  will  be  referred  to  again,  however,  under  induced  radioactivity » 
The  radioactivity  of  radium  is  much  superior  to  that  of  polonium; 
in  addition  to  the  A-rays  it  also  has  a  marked  activity  in  B-rays, 
and,  as  noted  before,  also  exhibits  luminous  or  visible  rays. 
A  radium-barium  chloride  containing  not  more  than  I  per  cent, 
of  radium  will  readily  affect  a  photographic  plate  in  one  minute,  and 
will  cause  fluorescence  in  a  barium-platinum  cyanide  screen  at  a  dis- 
tance of  several  decimeters. 
Radium  is  said  to  have  a  most  remarkable  effect  on  the  human 
eye.  If  a  vial  containing  radium  is  brought  near  the  closed  eye  of 
a  person,  it  will  cause  the  sensation  of  great  light.  This  peculiar 
effect  has  been  attributed  by  Giesel  to  phosphorescence  in  the 
vitreous  body.  Inflammatory  conditions  or  burns,  similar  to  those 
caused  by  the  X-rays,  have  also  been  caused  by  prolonged  exposure 
to  the  Becquerel  rays.  A  somewhat  similar  action  on  the  green 
leaves  of  growing  plants  has  also  been  noted.  By  prolonged  ex- 
posure the  chlorophyll  is  destroyed  and  the  leaf  turned  yellow 
without  killing  it. 
Beside  these  physiologic  actions  these  rays  also  have  chemical 
properties.  Air  is  ozonized ;  glass  is  colored  purple  or  dark  brown  ; 
salts  of  alkalies  are  colored ;  pure  sodium  sulphate,  for  instance,  is 
given  a  green  tint ;  but  when  contaminated  with  even  a  trace  of 
chloride  it  becomes  violet  instead. 
Anhydrous  radium  chloride  and  bromide  are  strongly  phosphores- 
cent and  emit  sufficient  light  to  make  them  visible  in  a  dark  room. 
This  phosphorescence  is  inherent  in  the  substance  and  not  caused 
by  extraneous  light  or  energy  as  in  the  case  of  calcium  sulphide. 
The  crystalline  salts  of  radium  are  not  as  strongly  phosphorescent, 
but  are  more  active  in  emitting  Becquerel  rays. 
Thorium  Rays. — Salts  of  thorium  have  radioactive  properties 
