198 
ACIDS  OF  RHUBARB  STALKS,  TOMATOES,  ETC. 
A  few  grains  of  the  crystals  were  burnt  and  the  residue  was 
proved  to  be  lime  by  dissolving  it  in  muriatic  acid,  and  precipi- 
tating it  with  oxalic  acid,  throwing  down  a  white  precipitate  of 
oxalate  of  lime  ;  thereby  proving  lime  to  be  the  base ;  this 
salt  then  obtained  by  the  process  for  malic  acid  appears  to  be 
acid  malate  of  lime. 
It  also  agrees  with  acid  malate  of  lime  in  its  atomic  propor- 
tion, as  207.5  is  the  equivalent  of  acid  malate  of  lime  in  the 
crystalline  state;  and  it  will  be  seen  by  the  following  experiment 
that  it  is  the  same  in  the  crystals  obtained  from  tomatoes. 
I  took  twenty  parts  by  weight  of  the  acid  malate,  and  burnt 
it  until  all  the  organic  matter  was  destroyed,  which  left  a  pro- 
duct of  two  and  a  half  parts,  being  about  one-eighth;  this  ex- 
periment may  indicate  pretty  clearly  that  the  crystallizable 
principle  in  tomatoes  is  acid  malate  of  lime,  associated  in  the 
juice,  as  appeared  afterwards,  with  citric  acid,  or  rather  with 
acid  citrate  of  potassa,  which  will  not  crystallize. 
My  attention  was  at  this  point  of  my  experiment  called  by 
Professor  Procter  to  an  analysis  of  the  tomato  by  Dr.  Plummer, 
published  in  the  Journal  of  Pharmacy,  vol.  23d,  page  165.  He 
examined  the  yellow  variety  of  tomatoes  and  detected  citric 
acid.  I  applied  his  tests  to  the  red  variety,  and  found  them  to 
produce  the  same  results,  from  which  I  have  no  doubt  at  all  that 
the  uncrystallizable  salt  exists  as  citrate  of  potassa  with  excess 
of  citric  acid. 
10.  One  pound  of  tomatoes  was  treated  as  before,  yielding 
eleven  ounces  of  juice ;  it  was  then  clarified  filtered,  and  neu- 
tralized with  ammonia,  which  produced  a  dark  wine-red  color ; 
it  was  then  evaporated  down  for  the  purpose  of  obtaining  dry 
citrate  of  ammonia,  but  owing  to  the  large  quantity  of  organic 
matter,  I  was  able  to  obtain  nothing  but  an  extract. 
Thus  failing  in  this  experiment,  I  was  unable  to  proceed  fur- 
ther in  arriving  at  the  definite  amount  of  citric  acid.  I  used 
other  alkalies  with  precisely  the  same  results. 
The  Quince. 
The  history  of  the  quince  (Cydonia  Vulgaris)  no  doubt  we  are 
well  acquainted  with,  being  cultivated  as  an  ornamental  tree  in 
