206 
ON  THE  APPLICATION  OF  DIALYSIS,  ETC. 
made  into  a  beverage,  it  is  thick  and  mucilaginous  ;  but  is  taste- 
less, odorless,  and  flavorless,  and  is  not  improved  by  roasting. — 
Lond.  Chem.  News,  Feb.  17,  1865. 
ON  THE  APPLICATION  OF  DIALYSIS  IN  DETERMINING 
THE  NATURE  OF  THE  CRYSTALLINE  CONSTITUENTS  OF 
PLANTS. 
By  J.  Attfield,  Ph.  D.,  F.  C.  S. 
Director  of  the  Laboratories  of  the  Pharmaceutical  Society  of  Great  Britain. 
[Read  at  the  Bath  Meeting  of  the  British  Pharmaceutical  Conference,  Sept.,  1864. 
Some  two  years  ago  ("Pharmaceutical  Journal"  for  March, 
1862)  I  published  the  results  of  an  examination  of  the  saline 
efflorescences  which  are  occasionally  found  on  medicinal  vege- 
table extracts.  These  crystalline  out-growths  were  found  to  be 
chloride  of  potassium  or  nitrate  of  potash.  The  former  salt 
had  often  been  observed,  but  the  latter  had  not  been  noticed  al- 
though it  is  of  common  occurrence.  From  that  examination,  it 
seemed  that  nitrate  of  potash  was  a  more  frequent  constituent 
of  plants  than  had  been  suspected,  and  I  then  proposed  the  ap- 
plication of  a  method  whereby  the  presence  of  it  and  of  similar 
salts  could  be  detected  in  the  fresh  plant.  The  suggestion  was 
to  dialyse  expressed  juices,  concentrated  decoctions  or  infusions 
of  plants,  and  then  to  evaporate  the  diffusate  to  a  small  bulk, 
when  it  was  to  be  expected  that  the  nitrate  of  potash,  or  any 
other  crystalline  salt,  would  separate  out  in  a  solid  and  recog- 
nizable form. 
Since  that  time  I  have  submitted  a  few  plant-juices,  the  first 
that  came  to  hand,  to  the  process,  and  have  obtained  results 
which  justify  me  in  recommending  the  method  as  one  likely  to 
be  of  great  service  in  the  study  of  vegetable  physiology.  Crys- 
talline salts  can  be  thus  obtained  which  would  inevitably  be  de- 
stroyed in  burning  a  plant  for  its  ash.  The  following  are  the 
details  of  the  experiments  : — 
Solanum  tuberosum. — A  few  pounds  of  potato  tops  were  col- 
lected and  at  once  crushed  and  pressed  and  the  juice  dialysed 
for  twenty-four  hours.  On  evaporating  the  diffusate  and  cooling, 
small  prismatic  crystals  separated,  having  all  the  physical  and 
chemical  characteristics  of  nitrate  of  potash.    Under  the  micro- 
