ACIDS  OF  RHUBARB  STALKS,  TOMATOES,  ETC. 
197 
persicum,  or  tomato,  was  grated  and  subjected  to  strong  expres- 
sion through  muslin  ;  which  produced  eleven  ounces  of  juice. 
The  dregs  were  treated  with  a  fresh  portion  of  water,  and  again 
pressed  ;  the  two  liquors  were  then  mixed  and  the  mucilaginous 
matter  precipitated  with  albumen,  boiling  the  juice  to  coagulate 
the  albuminous  matter.  It  was  then  filtered  and  allowed  to 
evaporate  slowly  by  means  of  a  water  bath  to  the  consistence  of 
a  thin  syrup,  and  set  aside  for  further  evaporation,  and  to  crys- 
tallize ;  but  on  examining  the  syrupy  liquid,  I  found  the  pro- 
cess of  crystallization  had  not  taken  place  as  I  anticipated,  pro- 
bably owing  to  the  thickness  of  the  acid  liquid,  by  which  I 
considered  it  impossible  to  crystallize  the  juice  alone. 
Suspecting,  from  the  action  of  the  juice  on  litmus  paper, 
its  not  being  a  free  acid,  but  existing  in  the  fruit  as  an  acid 
salt,  to  endeavor  to  ascertain  the  fact  more  precisely  I  pursued 
the  following  course. 
The  syrupy  liquid  from  the  above  experiment  was  placed  in  a 
crucible,  and  heat  applied  so  as  to  destroy  the  organic  matter 
of  the  extract.  The  incinerated  mass  was  then  treated  with  hot 
water,  so  as  to  dissolve  out  the  suspected  potassa ;  the  solution 
was  then  evaporated  to  dryness,  which  gave  as  the  result  eleven 
grains  of  a  white  powder,  which  appeared  to  be  carbonate  of  po- 
tassa, by  the  addition  of  a  few  drops  of  acetic  acid  liberating 
apparently  carbonic  acid. 
9.  I  proceeded  again  with  one  pound  more  of  tomatoes,  treat- 
ing it  in  the  same  manner  to  get  rid  of  the  albuminous  matter. 
I  precipitated  the  acid  liquor  with  a  concentrated  solution  of 
acetate  of  lead  and  washed  the  precipitate  thoroughly  with 
cold  water.  I  then  boiled  the  lead  salt  in  hot  water  a  few 
minutes,  it  was  then  thrown  on  a  filter  and  allowed  to  dry. 
The  precipitate  was  powdered  and  suspended  in  hot  water, 
and  this  raised  to  the  boiling  point,  and  while  still  hot  it  was 
decomposed  with  sulphuretted  hydrogen  and  the  precipitate 
thoroughly  washed  with  successive  portions  of  hot  water ;  the 
acidulous  liquor  was  then  evaporated  to  the  consistence  of  a  thin 
syrup,  and  allowed  to  crystallize.  On  examining  the  crystals  I 
found  their  form  to  be  six  sided  tables,  and  their  taste  somewhat 
like  cream  of  Tartar.  The  amount  of  crystals  from  one  pound 
of  the  fruit  was  only  ten  grains. 
