242 
BEHAVIOUR  OF  BORACIC  TO  TARTARIC  ACID. 
asserted  as  a  reason  for  its  alkaline  behaviour.  But  the  reac- 
tion of  alkalies  takes  place  immediately  with  a  brownish  red 
color,  assuming  a  violet  shade  on  drying,  or  even  disappearing 
entirely  after  some  time,  if  the  alkaline  solution  has  been  very 
weak  (lime  water) ;  the  brown  coloration  produced  by  boracic 
acid,  however,  takes  place  after  drying  the  paper;  though  char- 
acteristic, it  is  not  strong,  but  may  be  decidedly  deepened  by  pre- 
viously mixing  the  boracic  acid  with  a  stronger  acid,  such  as  hy- 
drochloric, nitric,  tartaric,  but  especially  dilute  sulphuric  acid, 
all  of  which  increase  the  coloration  more  than  acetic  and  other 
weaker  acids  ;  the  paper,  after  drying,  is  then  of  a  deep  red 
color. 
Curcuma  paper  is  turned  brown  instantly  by  a  solution  of 
borax,  the  color  fading  on  drying,  usually  leaving  a  reaction 
of  boracic  acid.  The  reaction  of  borax  therefore  is  similar  to 
that  of  a  weak  alkaline  solution  ;  but  it  ought  to  be  much 
stronger,  if  the  reactions  of  boracic  acid  and  the  alkalies  were 
occasioned  by  the  same  cause.  The  shade  of  the  reaction  by 
boracic  acid  mixed  with  another  acid  is  a  little  different  from 
that  by  pure  boracic  acid,  but  it  is  often  an  excellent  means  to 
discover  the  presence  of  small  quantities  of  borates. 
Though  somewhat  varying  in  the  shade,  similar  reactions  on 
curcuma  paper  are  obtained  by  solutions  in  strong  acids  of 
zirconia,  and  of  the  acids  of  the  following  metals  :  titanium,  tan- 
talum, niobium,  tin. — [Monatsber.  d.  Acad.  d.  Wissensch.  zu 
Berlin,  Bee.  1857.) 
Note  by  Prof.  A.  Buchner. — Several  years  ago,  Prof.  A.  Vo- 
gel,  jun.,had  drawn  attention  to  the  difference  between  the  reaction 
of  alkalies  and  boracic  acid  upon  curcuma  paper,  (Rep.  f.  Pharm. 
3d  ser.  iii.  178).  He  dilutes  a  tincture  of  curcuma  to  a  light 
yellow  color  and  adds  a  concentrated  solution  of  borax,  whereby, 
owing  to  the  alkaline  nature  of  the  salt,  a  brown  coloration  is 
produced,  reassuming  the  original  yellow  on  the  addition  of  sul- 
phuric acid  ;  if  more  sulphuric  acid  is  added,  boracic  acid  is 
liberated,  reacting  with  a  reddish  brown  color,  which  is  not 
changed  again  to  yellow  by  %  larger  quantity  of  sulphuric  acid. 
—(From  Neues  Bepert.  f.  Pharm.  1858.  193—197.) 
J.  M.  Mv 
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