MAGNESITE    DEPOSITS    OF    CALIFORNIA. 
THE  BURNING  OF  MAGNESITE. 
391 
Among  men  engaged  in  the  burning  of  magnesite  a  difference  of  opinion  has  existed 
as  to  the  temperature  at  which  the  carbon  dioxide  can  be  driven  off*  I  n  recent  experiments 
Herr  Otto  Brill  a  has  determined  this  point,  and  made  a  number  of  interesting  discoveries 
as  to  the  behavior  of  magnesite  when  heated.  His  experiments  were  carried  on  with 
carefully  prepared  and  purified  materials,  so  that  his  results  are  not  exactly  analogous 
to  those  that  would  be  obtained  by  using  the  raw  natural  material.  He  showed  that, 
while  calcium  carbonate  (as  ordinary  limestone)  gives  up  all  of  its  carbon  dioxide  at  825°  C. 
(1,517°  F.),  when  magnesium  carbonate  (magnesite)  is  burned  it  begins  to  give  off  carbon 
dioxide  at  about  235°  C.  (455°  F.);  little  if  any  more  carbon  dioxide  seems  to  be  given  off 
while  the  material  is  held  at  255°  C,  but  on  raising  the  temperature  the  gas  is  again  given 
off.  Other  such  stages  were  marked  at  various  points,  and  these  were  considered  to  show 
the  successive  formation  and  breaking  up  of  various  basic  carbonates.  The  last  of  the 
carbon  dioxide  is  given  off  at  510°  C.  (950°  F.),  a  temperature  much  below  that  needed  to 
burn  lime.  Herr  Brill's  table  showing  the  different  carbonates  is  given  below.  The  fifth 
column,  the  reduction  to  the  Fahrenheit  measurement  of  temperature,  is  added  by  the 
writer  of  this  paper. 
Basic  carbonates  formed  in  burning  magnesite. 
Calcu- 
lated 
MgO. 
10MgO.9CO 
9Mg0.8C02 
8Mg0.7C02 
7Mg0.6C02 
6Mg0.5C02 
5Mg0.4C02 
7MgO.C02. 
Per  cent. 
50. 64 
50.79 
51.20 
51.51 
52.  36 
53.41 
86.  53 
Ob- 
tained. 
MgO. 
Per  cent. 
50. 58 
50.  j8 
51.37 
51.69 
52.  35 
53. 03 
S6.31 
Dissociation 
temperature. 
°r. 
265 
295 
325 
340 
380 
405 
510 
F. 
509 
563 
617 
644 
716 
761 
950 
The  temperature  at  which  magnesite  gives  up  the  last  of  its  carbon  dioxide,  510°  C,  is 
below  a  red  heat,  but  the  time  required  to  drive  off  all  of  the  gas  is  not  given,  and  this,  of 
course,  would  vary  with  the  size  of  the  material  used.  The  important  point,  however,  is 
that  at  this  temperature  all  of  the  carbon  dioxide  may  be  driv(  n  off,  so  that,  although 
higher  heating  will  undoubtedly  remove  the  gas  more  quickly,  it  ordinarily  means  a  waste 
of  fuel. 
MANUFACTURE  OF  LIQUID  CARBON  DIOXIDE. 
At  the  time  of  the  writer's  visit  the  Western  Carbonic  Acid  Gas  Company  of  San  Fran- 
cisco, with  works  across  the  bay  at  Sedan  or  Emeryville,  was  the  only  manufacturer  of 
carbonic-acid  gas  from  magnesite,  although  one  of  the  subsidiary  companies  of  the  Ameri- 
can Magnesite  Company  was  erecting  a  plant  at  East  Oakland  (Clinton). 
The  magnesite  is  burned  in  a  kiln  with  one-tenth  its  weight  of  coke,  and  the  gas  is  pumped 
into  scrubbers,  of  which  there  are  three,  filled  with  broken  limestone  to  counteract  any 
sulphuric  acid  formed,  and  washed  with  sea  water.  The  gas  then  passes  to  an  absorption 
tower,  where  it  comes  in  contact  with  a  sprayed  solution  of  potassium  carbonate,  by  which 
it  is  absorbed.  The  "loaded  solution"  is  then  pumped  into  boilers,  where  it  is  raised  to  a 
temperature  just  below  the  boiling  point  of  water.     The  solution  giv<  s  up  its  gas  and  is 
oUeber  die  Dissoziation  der  Karbonate  der  Erdalkalien  und  des  Magnesiumkarbonates:  Zeitschrift 
fur  Anorganische  Chemie,  Band  45,  Heft  3,  June,  1905,  pp.  277-292. 
