430         The  Interaction  of  Borax,  Carbonates,  etc. 
The  acidity  is  unquestionably  due  to  the  transformation  of  the 
borax  into  sodium  metaborate  and  boric  anhydride,  the  latter  unit- 
ing with  water  to  form  boric  acid.  As  significant  evidence  sub- 
stantiating the  above  statement,  may  be  noted  that  no  acid  reaction 
results  in  the  absence  of  water,  for  on  using  anhydrous  borax, 
anhydrous  glycerin  and  elevating  the  temperature  so  as  to  expel 
the  water  formed  during  the  reaction,  no  acid  reaction  results. 
A  support  to  the  above  composition  of  borax  may  be  found  in 
the  formation  of  tetraboric  acid.  When  orthoboric  acid  is  heated 
there  are  formed  at  ioo°  C.  metaboric  acid  and  water — H3BOs  = 
HB02  -f  H20;  at  1600  C.  it  yields  tetraboric  acid  and  water — 
4  HsB03  =  H2B407  -f  5  H20 ;  at  a  still  higher  temperature  all 
the  water  is  eliminated  and  boric  anhydride  is  formed — H2B407  = 
2  B203  +  H20. 
Tetraboric  acid  is  the  intermediate  compound  from  which  only  a 
portion  of  the  water  has  been  eliminated ;  that  is,  it  is  neither 
metaboric  acid  nor  boric  anhydride,  but  a  mixture  of  the  two.  In 
that  borax  is  a  salt  of  tetraboric  acid  it  must  necessarily  share  an 
analogous  composition.  Direct  evidence  that  borax  is  so  consti- 
tuted is  insufficient  but  indirect  evidence  appears  to  be  ample. 
The  avidity  of  boric  acid  is  unity  when  nitric  acid  is  taken  as  one 
hundred.  Boric  acid  displaces  carbonic  acid,  and  vice  versa,  depend- 
ing on  the  conditions ;  consequently  the  avidity  of  carbonic  acid 
must  be  about  unity. 
It  appears  to  be  well  established  that  the  acidity,  above  referred 
to,  is  due  to  boric  acid ;  therefore  all  carbonates  transposable  by 
this  acid  will  evolve  carbon  dioxide  with  the  simultaneous  forma- 
tion of  sodium  metaborate  and  sodium  orthoborate  when  mixed 
with  borax  and  glycerin. 
The  following  equations  present  the  facts  in  a  most  lucid  manner : 
(1)  2C3H5(OH)3  +  Na2B407  =  2C3H5B03  +  2NaB02  +  3H20. 
(2)  2C3H5(OH)3  +  Na2B407  +  3H20  =  2C3H5(OH)3  +  2H3B03  + 
2NaB02. 
(3)  C3H5B03  +  3H20  =  C3H5(OH)3  +  H3B03. 
(4)  3Na2C03  +  2H3B03 .=  2Na3B03  +  3C02  +  3H20. 
The  first  equation  represents  the  reaction  when  there  is  no  water 
present,  that  formed  being  expelled  by  heat ;  the  second  when 
water  is  present ;  the  third  the  action  of  water  on  boroglycerol,  and 
the  last  simply  the  action  of  boric  acid  on  an  alkaline  carbonate. 
