156 
WOOD  SPIRIT  AND  ITS  DETECTION. 
manner,  gave  the  reaction  very  strongly.  Some  solution  of 
chloride  of  mercury  and  a  few  drops  of  the  naphtha  were 
mixed,  and  then  excess  of  potash  added,  which  caused  the  reso- 
lution of  the  oxide  of  mercury  without  the  aid  of  heat.  A  por- 
tion of  this  solution,  cn  the  cautious  addition  of  an  acid,  did  not 
give  any  precipitate.  The  mixture  was  now  gently  warmed, 
and  afterwards  acetic  acid  added,  upon  which  a  precipitate  was 
immediately  formed. 
From  the  results  of  these  experiments,  the  following  informa- 
tion may  be  gleaned: — 1st.  That  the  compound  in  question  is 
somewhat  resinoid  in  character  and  destitute  of  crystalline 
structure ;  2ndly.  It  is  precipitated  by  boiling,  or  on  the  addi- 
tion of  an  acid  ;  3rdly.  It  is  easily  decomposed  by  hydrochloric 
acid,  the  organic  body  passing  off  unchanged ;  and  4thly.  It  is 
always  necessary  to  employ  heat  previous  to  the  addition  of  an 
acid,  otherwise  no  precipitate  will  be  produced  immediately.  A 
consideration  of  the  first  of  these  points,  viz.,  the  want  of  crys- 
talline structure,  the  gelatinous  appearance,  and,  in  fact,  the 
colloidal  nature  of  the  compound  in  question,  led  me  to  resort 
to  the  beautiful  principle  of  "dialysis,"  as  a  means  of  freeing 
its  solution  from  all  saline  impurities.  In  order  to  put  this  idea 
to  the  test  of  experiment,  some  of  the  mercurial  solution  was 
placed  on  a  dialyser,  floating  on  a  considerable  bulk  of  distilled 
water.  After  twenty-four  hours,  the  diffusate  contained  a 
large  quantity  of  chlorine,  and  but  a  very  small  proportion  of 
mercury.  The  diffusion  was  then  allowed  to  continue  for  eight 
days,  during  which  time  the  water  was  changed  twice  a  day. 
On  the  ninth  day  a  mere  trace  of  chlorine  could  be  detected  in 
the  diffusate,  and  but  little  mercury.  The  liquid  on  the  dialy- 
ser was  almost  odorless  and  colorless,  and  of  high  specific 
gravity ;  it  was  neutral  to  test-papers,  and  gave  a  copious  pre- 
cipitate both  on  boiling  and  the  addition  of  acetic  acid, 
thus  demonstrating  that  the  original  compound  was  still  present 
in  the  solution,  apparently  unchanged. 
In  my  subsequent  experiments  I  have  found  this  method  of 
separation  most  valuable,  since  it  enables  me  to  easily  purify 
the  colloidal  mercurial  compound  from  the  crystalloids  which 
accompany  it  in  solution.  The  recapitulation  of  these,  my 
earliest  experiments,  is  sufficient  to  show  the  more  important 
