508  Chemistry  of  Tartaric  and  Citric  Acid.        { ^""ocT'iSs*'"'*' 
acid  is  also  present  Chem.  Soc.  J./'  1875,  931).  The  whole  of  the 
free  and  combined  acid  in  lemon  juice  is  not,  however,  citric  acid. 
The  method  employed  in  the  Millwall  Laboratory  for  determining 
the  amount  of  citric  acid  present,  or  rather  the  amount  of  organic  acid 
capable  of  yielding  an  insoluble  calcium  salt,  has  been  already 
described  {Ibid,,  934).  The  juice  is  exactly  neutralized  with  soda,  an 
excess  of  calcium  chloride  added,  and  the  calcium  citrate  precipitated 
by  boiling  in  a  salt  or  glycerin  bath.  The  precipitate  is  collected  and 
washed  with  hot  water.  The  filtrate  and  washings  are  neutralized 
with  dilute  ammonia,  and  concentrated  in  the  bath  to  a  small  bulk ; 
the  second  precipitate  thus  obtained  is  also  collected  and  washed. 
Mr.  Grosjean  was  in  the  habit  of  concentrating  yet  a  second  time,  and 
collecting  a  third  precipitate,  if  any.  The  precipitates  are  finally 
ignited,  and  the  citric  acid  originally  present  calculated  from  the 
neutralizing  power  of  the  resulting  carbonate  of  calcium.  Working 
in  this  way,  with  1  gram  of  citric  acid,  Mr.  Grosjean  obtained  99'6 
per  cent,  of  the  acid  taken. 
In  Table  II  (p.  509)  will  be  found  determinations  of  free  acid,  and 
of  precipitable  acid,  made  by  Mr.  Grosjean  in  commercial  samples  of 
concentrated  lemon  and  other  juices;  the  acid  found  is  in  all  cases 
calculated  as  citric  acid  : 
It  appears  from  the  figures  given  in  the  table  that  the  precipitable  acid 
in  commercial  concentrated  Lemon  juice  is,  on  an  average,  very  nearly 
equal  in  quantity  to  the  free  acid  present ;  in  65  analyses,  representing 
895  pipes,  the  precipitable  acid  averages  99*2  per  cent,  of  the  free.  There 
is,  however,  occasionally  a  somewhat  considerable  range  of  variation, 
as  will  be  seen  from  the  figures  showing  the  highest  and  lowest  pro- 
portion of  precipitable  acid  found  in  the  65  saipples.  In  , two  excep- 
tional samples  of  juice,  A  and  B,  representing  together  27  pipes,  the 
proportion  of  precipitable  acid  is  much  lower ;  and  in  one  sample, 
representing  25  pipes,  not  mentioned  in  the  table,  as  it  seemed  to  lie 
intermediate  between  lemon  juice  and  bergamot,  the  precipitable  acid 
was  only  81*1  per  cent,  of  the  free.  There  can  be  no  doubt,  there- 
fore, that  the  method  of  precipitation  ought  to  be  adopted  in  all  valu- 
ations of  commercial  lemon  juice. 
The  analyses  of  concentrated  Bergamot  juice  are  much  fewer;  the 
proportion  of  precipitable  to  free  acid  appears  very  similar  to  that  in 
lemon  juice. 
