100  On  Practical  Pharmacy,  {  MarcTi-.m^ 
cases.  The  Pharmacopoeia  processes  for  hydrocyanic,  valerianic  and 
benzoic  acids  may  be  performed  by  starting  the  processes  before  the 
lecture,  without  materially  wasting  the  professor's  hour. 
It  is  quite  possible,  by  mixing  powdered  galls  with  ether  and  moist- 
ure beforehand,  to  express  the  liquid  tannin,  and  dessicate  it  on  tin 
plates  before  the  class  in  a  very  few  minutes,  so  as  to  produce  good 
commercial  tannin.  There  is  no  difficulty  in  making  collodion  cotton, 
washing  and  drying  it  by  aid  of  alcohol,  and  dissolving  it  in  ether, 
while  describing  the  process  and  substances. 
The  rapid  preparation  of  hydrated  sesquioxide  of  iron,  fit  for  an 
antidote,  should  be  shown  to  encourage  the  student  to  do  it  dex- 
terously. The  processes  for  many  metallic  and  other  chemical  prepa- 
rations may  be  partially  illustrated,  but  as  a  general  rule  the  time  of 
the  lecturer  is  better  spent  in  pointing  out  any  difficulties  requiring 
precautions  than  in  attempting  to  go  further,  in  all  cases  when  pos- 
sible speaking  from  his  own  knowledge. 
The  processes  for  the  more  important  alkaloids  may,  by  exhibiting 
them  at  difierent  stages,  be  well  explained  to  a  class,  but  it  involves 
much  time  and  careful  preparation.  It  is  also  quite  proper  to  give 
the  demonstrative  tests  of  purity,  and  of  recognition  as  well,  though 
this  is  usually  the  work  of  the  Materia  Medica  professor. 
In  regard  to  vegetable  drugs,  their  relation  to  solvents  can  be 
easily  demonstrated  by  percolation,  and  many  of  the  more  important 
should  be  the  subject  of  practical  experiments  to  prove  that  these  sol- 
vents effectually  remove  the  essential  constituents.  It  is  an  excellent 
plan  to  exhibit  as  many  as  possible  of  the  important  constituents  of 
drugs,  to  make  the  remarks  more  impressive.  This  hint  especially 
applies  to  such  drugs  as  jalap,  scammony,  rhubarb,  cinchona,  ipecac, 
opium,  aloes,  cantharis,  colocynth,  hyoscyamus,  nux  vomica,  etc. 
In  his  lectures  on  preparations  like  mixtures,  pills,  liniments,  muci- 
lages, suppositories,  ointments,  etc.,  the  professor  will  have  a  wide 
scope  for  interesting  suggestions  and  cautions  bearing  on  extempora- 
neous pharmacy,  which  should  never  be  lost  sight  of  in  every  step  of 
the  course.  As  an  instance  of  what  we  mean,  let  the  subject  be  gum 
Arabic  in  its  relation  to  pharmacy.  He  might  say  that  it  is  a  lime 
salt  of  arable  acid  (which  he  proves  by  means  of  oxalate  of  ammonia,) 
that  it  is  very  soluble  in  water,  and  insoluble  in  alcohol,  ether,  chloro- 
form, benzin,  turpentine,  and  all  the  volatile  and  fixed  oils,  precipitable 
by  subacetate  but  not  by  neutral  acetate  of  lead,  and  in  strong  solution 
