488  Analysis  of  Coal  lar  Preparations.   {^£gS*i$£  ' 
chloride.  The  greater  portion  of  the  ether  is  distilled  off  on  the 
water-bath,  and  the  oily  residue  introduced  with  the  aid  of  a  little 
ether  into  a  small  weighed  distillation  flask  with  side  tubulure  in 
the  neck. 
On  distillation  with  a  free  flame  the  temperature  in  the  flask, 
measured  by  a  thermometer  the  bulb  of  which  should  be  above  the 
level  of  the  boiling  fluid,  remains  under  400  or  45 0  C.  until  the  last 
traces  of  ether  have  distilled  over.  The  temperature  then  suddenly 
rises  to  ioo°,  1500,  or  even  2000  C,  according  to  the  character  or" 
the  coal-tar  oil  that  has  been  employed,  and  the  hydrocarbons  then 
commence  to  distil  over. 
The  hydrocarbons  that  distil  below  2000  C.  are  generally  of  a 
limpid  fluid  character,  but  the  fraction  slightly  above  that  tempera- 
ture frequently  solidifies  owing  to  the  presence  of  naphtalene,  whilst 
above  2500  C.  the  hydrocarbons  that  distil  over  are  again  of  a  liquid 
character,  though  distinctly  viscous.  Above  3000  C.  the  distillation 
may  be  discontinued  and  the  three  fractions  indicated  weighed,  as 
well  as  the  undistilled  portion  in  the  flask,  which  generally  becomes 
solid  on  cooling  from  the  presence  of  anthracene  and  phenanthrene. 
The  total  weights  give  the  amount  of  hydrocarbons  in  50  grammes 
of  the  preparation,  or  multiplied  by  two  the  percentage.  Not  only 
does  the  amount  and  composition  of  the  hydrocarbons  vary  much 
in  different  preparations,  according  to  the  degree  of  dilution  and 
different  tar  oils  employed,  but  the  relation  between  amount  of 
hydrocarbons  and  tar  acids  present  in  the  preparations  examined  by 
us  was  also  found  to  be  very  variable,  ranging  from  equal  parts  of 
hydrocarbons  and  acid  constituents  in  standard  fluids  to  20  parts 
hydrocarbons  to  I  part  acids  in  other  preparations,  which  are  con- 
sequently of  inferior  disinfectant  value. 
Although  the  hydrocarbons,  especially  those  of  higher  boiling 
points,  have  a  distinct  antiseptic  and  disinfectant  value,  yet  the  tar 
acids,  consisting  principally  of  carbolic  acid  and  the  cresols,  gener- 
ally referred  to  under  the  name  of  cresylic  acid,  it  is  well  known 
possess  these  properties  to  a  far  higher  degree.  The  value  of  coal- 
tar  preparations  as  disinfectants  in  fact  depends  to  a  large  extent  on 
the  amount  of  tar  acids  present. 
Determination  of  Acid  Constituents. — The  tar  acids,  including  as 
they  do  phenol  and  its  homologues,  are  not  generally  acids  in  the 
true  chemical  sense  of  the  word,  but  so  far  partake  of  an  acidic 
