Am.  Jour.  Pharm.  \ 
Sept.,  1883.  J 
Folyhydric  Alcohols  and  Borax. 
455 
alkalinity  is  reproduced  by  heating  but  is  again  destroyed  as  the  tem- 
perature of  the  solution  is  lowered.  Water  also  is  able  to  annihilate 
the  acidity  and  reproduce  the  alkalinity  of  the  liquid.  Now  when 
sodium  metaborate  or  pyroborate  is  dissolved  in  water  dissociation 
occurs,  resulting  in  the  formation  of  an  acid  borate  or  boric  acid  and 
the  liberation  of  free  alkali  hence  the  alkalinity  of  such  solutions. 
Upon  adding  acid  in  sufficient  quantity  to  neutralize  this  alkalinity,  a 
stable  neutral  system  is  the  result.  The  addition  of  more  water  dis- 
turbs this  system  of  neutrality,  by  producing  further  dissociation  of 
the  salt  indicated  by  renewed  alkalinity.  A  rise  of  temperature  pro- 
duces in  this  neutral  solution  the  same  effect  as  excess  of  water,  namely, 
alkalinity,  which,  however,  disappears  as  the  solution  cools,  the  heated 
water  effecting  dissociation,  and  recombination  occurring  as  the  liquid 
€ools. 
If  excess  of  acid  be  added  no  change  is  observed  upon  heating, 
doubtless  because  acid,  and  therefore  more  stable,  salts  are  produced. 
It  follows  from  these  experiments  that  when  a  polyhydric  alcohol  is 
added  to  an  aqueous  solution  of  sodium  pyroborate  in  quantity  just 
sufficient  to  produce  an  acid  reaction  due,  as  Ave  have  previously  seen, 
to  the  liberation  of  boric  acid  from  some  of  the  sodium  pyroborate 
with  formation  of  sodium  metaborate,  upon  the  addition  of  more  water 
or  application  of  heat  dissociation  of  the  undecomposed  sodium  pyro- 
borate and  metaborate  takes  place,  liberating  alkali  in  quantity  more 
than  sufficient  to  neutralize  the  free  acid,  hence  the  liquid  is  alkaline. 
As  the  temperature  is  lowered  recombination  takes  place  with  the  con- 
sequent regeneration  of  the  original  neutrality  or  faint  acidity.  If 
excess  of  the  polyhydric  alcohol  be  added,  that  is,  more  than  enough 
to  render  the  liquid  neutral  or  faintly  acid  no  reaction  is  produced 
upon  the  heating,  evidently  because  excess  of  boric  acid  has  been  set 
free. 
General  Considerations. — The  chief  result  of  this  inquiry  is  to  show 
that  polyhydric  alcohols  decompose  sodium  pyroborate  with  the  for- 
^  Berth elot  has  shown  ("Essai  de  M6canique  Chimique,"  vol.  ii,  225) 
that  increased  addition  of  water  produces  increased  dissociation ;  thus  when 
boron  trioxide  combines  with  sodium  oxide  to  form  sodium  metaborate 
{BjOg+NaaO)  in  presence  of  220  molecules  of  water,  11-75  heat  units  are 
liberated. 
BaOa+Na-iO  in  presence  of  330  H^O  liberates  11-56  h.u. 
BjOg+NaaO  in  presence  of  440  H2O  liberates  11-13  h.u. 
BaOa+Na^O  in  presence  of  1320  H2O  liberates  10-91  h.u. 
