SULPHO-CARBOLIC  ACID  AND  THE  SULPHO-CARBOLATES.  133 
is  very  convenient  for  obtaining  the  salts  of  other  bases  by 
double  decomposition  with  their  sulphates,  the  baryta  being  re- 
moved by  the  filter  as  sulphate. 
According  to  E.  Menzner  (Chem.  News,  Jan.  3,  1868,  p.  10), 
this  acid  is  prepared  by  heating  equal  equivalents  of  carbolic 
acid  and  sulphuric  acid  in  a  water  bath,  diluting,  after  standing 
twenty-four  hours,  with  water,  neutralizing  with  carbonate  of 
lead,  filtering  and  decomposing  the  plumbic  sulpho-carbolate 
with  hydrosulphuric  acid,  and  carefully  concentrating  the  filtered 
solution  first  by  heat  and  afterwards  in  a  dessicator. 
For  the  purposes  of  the  pharmaceutist,  Mr.  C.  H.  Wood  re- 
commends the  direct  saturation  of  the  crude  acid  (formed  by 
mixing  two  volumes  of  pure  carbolic  acid  with  one  volume  of  oil 
of  vitriol  in  a  glass  flask,  and  heating  the  mixture  to  290°  F. 
for  five  minutes,  allowing  it  to  cool,  and  diluting  with  six  or 
eight  volumes  of  water)  with  the  bases  or  their  carbonates,  and 
depending  on  crystallization  to  purify  them.  In  this  mixture 
there  is  a  portion  of  uncombined  sulphuric  acid,  which  makes  it 
necessary  to  purify  all  but  the  first  crystallization  by  treatment 
with  alcohol,  to  separate  the  insoluble  sulphates.  It  appears  to 
us  that  there  is  a  loss  sustained  by  this  process,  a  portion  of  the 
carbolic  acid  is  also  uncombined,  and  that  after  mixing  the  acids 
and  heating  them  it  is  better  to  allow  them  to  stand  twenty-four 
hours  before  saturating.  This  is  the  plan  we  have  adopted  in 
making  the  soda,  zinc,  and  magnesia  salts.  When  the  acids  are 
mixed  a  reddish  color  is  developed,  which  grows  deeper  by  stand- 
ing, and  stains  the  salts  a  light  rose  color.  Laurent  notices  this 
peculiarity.  In  adopting  the  baryta  process  this  is  avoided  in 
great  measure.  Dr.  Hoffmann  prepared  his  salts  from  the  baryta 
salt,  which  he  made  "  by  digesting  in  a  water  bath,  at  a  tem- 
perature near  the  boiling  point  of  water,  a  mixture  of  equal 
weighli^parts  of  crystallized  and  previously  melted  phenol  (car- 
bolic acid)  and  sulphuric  acid  sp.  gr.  1-84  during  forty- eight 
hours,  or  until  the  mixture  formed  a  clear  solution  with  water. 
The  acid  mixture  is  then  diluted  with  an  equal  bulk  of  water, 
and  gradually  added  to  freshly  precipitated  carbonate  of  baryta 
suspended  in  water  until  the  carbonate  is  nearly  all  dissolved, 
when  the  solution  of  sulpho-phenate  of  baryta  is  ready  for  use." 
