278 
eochleder's  proximate  analysis. 
it  is  possible,  by  this  method,  we  have  still  to  ascertain  whether  only  ahydro- 
carbon,  or  a  mixture  of  several  hydrocarbons,  is  j^resent.  To  arrive  at  a  con- 
clusion on  this  point,  the  oil  in  question  is  distilled  in  a  small  retort  in 
which  a  thermomster  is  inserted.  A  rapid  continued  rising  of  the  boiling 
point  proves  that  the  oil  is  a  mixture  of  several  volatile  substances. 
It  should  be  always  observed  whether  a  portion  of  the  original  oil,  as  it 
floats  on  the  watery  distillate,  or  falls  to  the  bottom  of  the  same  as  a  layer, 
cannot  be  congealed  by  exposure  to  very  low  temperatures,  independently 
of  its  reactions  and  other  properties.  ^Yii(\\iQni\'^  a  partial  separation,  sim- 
ply by  exposure  to  cold,  may  be  effected  in  substances  of  that  kind,  more 
readily  in  this  than  in  any  other  way. 
In  winter,  the  most  convenient  method  is  to  stick  a  test  tube  containing 
the  oil  in  a  beaker  glass  filled  with  snow,  andto  stand  the  whole  in  a  wood- 
en vessel.  The  space  between  the  glass  and  the  wood  vessel  is  filled  with  saw- 
dust ;  the  glass  should  stand  on  a  layer  of  sawdust  several  inches  high;  into 
the  glass,  alcohol  is  poured  carefully,  when  the  snow  melts,  and  the  mixture 
cools  down  to  13°  Fahr.  below  zero.  The  whole  is  covered  with  a  quire  of 
filtering  paper.  As  paper  and  sawdust  are  bad  conductors  of  heat,  the  de- 
pressed temperature  continues  sufficiently  long  to  congeal  the  oil  or  to 
cause  the  separation  of  solid  substances  from  it  when  this  can  be  accom- 
plished by  cold. 
Besides  the  volatile  bodies  just  under  consideration,  which  in  the  form 
of  oils  can  be  separated  on  the  surface  or  at  the  bottom  of  the  distillate, 
there  exists  still  a  class  of  bodies  which  in  their  composition  are  readily 
distinguished  from  those  spoken  of.  These  are  the  essential  oils  contain- 
ing sulphur,  as  they  are  generally  termed  ;  for  example,  oil  of  mustard, 
oil  of  onion,  oil  of  assafetida,  oil  of  garlic,  &c.  The  presence  of  these  oils 
is  generally  rendered  evident  by  their  odor.  But  to  be  certain  as  regards 
their  absence  or  presence,  a  portion  of  the  oil  is  oxidized  with  nitric  acid, 
and  then  tested  for  sulphuric  acid.  If  sulphur  is  contained  in  the  oil,  it 
is  converted  into  sulphuric  acid  by  treatment  with  nitric  acid,  which  can 
be  detected  by  nitrate  of  baryta.  The  majority  of  these  oils  affords  preci- 
tates  when  dissolved  in  alcohol  and  mixed  with  a  solution  of  bichloride  of 
platina  or  bichloride  of  mercury.  By  the  application  of  platina  of  bichloride 
the  precipitates  are  either  pure  red,  reddish-yellow,  brownish  yellow  or 
reddish  brown  ;  and  by  the  use  of  bichloride  of  mercury,  on  the  contrary, 
w^hite,  sometimes  with  a  shade  of  yellow. 
It  still  remains  to  be  stated  liow  the  alcoholic  solutions  of  ethereal  oils 
must  be  treated,  as  obtained  when  an  oil  is  treated  with  alkaline  bisul- 
phites, and  thereby  partly  congealed,  and  the  fluid  portion  remaining  re- 
moved from  the  solid  compound  by  washing  with  alcohol. 
Such  a  spirituous  solution  is  shaken  with  milk  of  lime,  and  in  a  closed 
vessel  allowed  to  remain  undisturbed  until  the  insoluble  portion  is  depo- 
sited at  the  bottom.  The  clear  fluid  is  taken  off  and  distilled,  to  the  distil- 
late i3  added  a  piece  of  anhydrous,  but  not  fused,  chloride  of  calcium,  after 
