198  Lycopersicum  Esculentum — -Tomato.  {A\Ja7T,m2RM' 
it  available  as  a  commercial  source  of  the  acid.  The  variety  on  which 
I  operated  was  the  red  tomato  known  in  market  as  the  "Tilden''; 
this  is  quite  solid,  of  a  medium  size,  and  contains  comparatively  little 
juice.  There  are  other  inferior  varieties  which  contain  a  larger  amount 
of  juice  and  have  more  acidity  of  taste,  and  I  expect  these  would  be 
found  to  contain  a  larger  proportion  of  acids  ;  but  being  at  the  time 
unable  to  procure  any  of  them  I  was  obliged  to  content  myself  with 
an  examination  of  the  variety  named. 
I  have  employed  two  processes  in  my  examination,  the  first  being 
mainly  that  given  in  the  British  Pharmacopoeia  for  the  preparation 
of  citric  acid  from  lemon  juice. 
One  gallon  of  juice,  freshly  expressed  from  fully  ripe  tomatoes, 
was  heated  to  the  boiling  point  and  strained.  Keeping  it  at  about 
200°  F.,  powdered  chalk  was  added  until  effervescence  ceased.  After 
cooling,  the  precipitate  was  separated  by  straining  and  filtration,  and 
mixed  with  two  pints  of  water.  To  the  mixture  was  gradually  added 
three  pints  of  water,  mixed  with  four  fluidounces  of  sulphuric  acid, 
some  effervescence  being  produced,  probably  due  to  an  excess  of  cal- 
cium carbonate.  The  mixture  was  boiled  gently  for  half  an  hour  and 
filtered.  The  filtrate,  after  partial  evaporation,  was  set  aside  to  allow 
any  calcium  sulphate  which  might  be  present  to  crystallize.  After 
standing  twenty-four  hours  the  liquid  was  decanted — there  being  a 
slight  sediment  but  no  crystals — and  evaporated  until  a  slight  film 
began  to  form  on  the  surface,  when  it  was  again  set  aside. 
After  standing  about  three  weeks  there  was  a  considerable  deposit 
of  brown  extractive  matter,  having  a  crystalline  appearance,  from 
numerous  small  crystals  imbedded  in  it.  As  this  extractive  evi- 
dently retarded  the  formation  of  crystals,  and  being  pressed  for  time, 
I  continued  the  evaporation,  at  a  gentle  heat,  until  the  whole  was 
reduced  to  the  consistence  of  an  extract,  which  I  brought  with  me  on 
my  return  to  the  College,  for  further  examination. 
Upon  resuming  operations  in  the  laboratory  of  the  College,  I  first 
made  a  preliminary  examination  of  a  small  portion  of  the  mass,  ac- 
cording to  the  method  directed  in  Will's  tables,  and  found  present 
citric,  malic  and  oxalic  acids.  In  order  to  isolate  them,  the  mass  was 
boiled  with  a  sufficient  quantity  of  water,  and  the  solution  filtered. 
A  small  quantity  of  inert  matter  was  left  undissolved.  The  filtrate 
was  neutralized  with  calcium  hydrate,  and  the  precipitate  separated 
by  filtration,  and  reserved. 
