AmNovri887?rm'}      Commercial  Carbolic  Compounds.  585 
and  the  amount  of  this  will  give  the  tar-oils,  etc.,  present  in  the 
sample.  Provided  there  is  no  excess  of  water,  this  amount  is  deducted 
from  20  cc,  and  the  difference  multiplied  by  five  gives  the  percentage 
strength  of  the  sample.  Excess  of  water  (which  is  of  very  rare  occur- 
rence) is  best  ascertained  by  adding  some  of  the  sample  to  three  times 
its  volume  of  benzol,  when  it  should  dissolve  quite  clear  if  there  be 
no  such  excess. 
Case  2.  The  sample  is  not  darker  than  pale  sherry. — Try  if  it  dis- 
solves nearly  clear  in  four  times  its  volume  of  5  per  cent,  solution  of 
sodium  hydrate,  and  if  so,  it  may  be  taken  as  practically  free  from 
tar-oils.  If  not,  treat  it  as  above,  using  however,  only  a  very  small 
fixed  volume  of  the  benzol.  This  acid  is  apt  to  contain  excess  of 
water,  which  must  be  estimated  by  shaking  20  cc.  of  the  sample  in 
the  "  carbolimeter"  with  80  cc.  of  saturated  solution  of  sodium  chlo- 
ride, and  observing  the  diminution  in  volume  that  will  take  place  if 
such  excess  be  present. 
A  fair  idea  as  to  whether  the  acid  is  chiefly  phenol  or  cresol  may 
always  be  obtained  by  applying  the  bromine  reaction,  and  observing 
the  nature  of  the  precipitate. 
(4)  EXAMINATION  OF  A  SAMPLE  OF  PURE  CARBOLIC  ACID  IN  THE 
LIQUEFIED  FORM. 
In  examining  samples  of  this  acid,  specific  gravity  practically  goes  for 
nothing.  The  points  to  determine  are  : — (1)  That  it  should  entirely 
dissolve  to  a  perfectly  clear  solution  in  four  times  its  volume  of  5 
per  cent,  solution  of  sodium  hydrate  ;  (2)  That,  when  shaken  with  an 
excess  of  saturated  solution  of  sodium  chloride,  as  already  described, 
it  suffers  no  diminution  in  volume ;  (3)  When  treated  with  bromine 
water  in  excess  it  gives  a  fine  curdy  precipitate,  not  at  all  inclined  to 
stick  to  the  tube. 
Photoxylin,  a  substance  in  use  amongphotographers,  was  recommended 
some  time  ago  by  Dr.  Krysinski  as  a  suitable  material  for  mounting  micro- 
scopic specimens,  and  more  recently  still  it  has  been  utilized  by  Professor 
Wahl,  of  St.  Petersburg  (Lancet,  June  18,  1887),  in  surgical  practice.  A  five 
per  cent  solution  in  equal  parts  of  alcohol  and  ether  he  finds  preferable  to 
collodion,  as  it  adheres  more  firmly  to  the  skin,  not  being  so  easily  rubbed 
off  in  washing.  It  is  absolutely  impervious  to  liquids,  and  exerts  a  perfectly 
even  compression  on  the  tissues.1 
i  Gun  cotton  soluble  in  a  mixture  of  equal  parts  of  alcohol  and  ether.  -Editor. 
