Am-  Jour.  Pharm.  \ 
Jan.  1, 1872.  j 
Essential  Oil  of  Mustard  Seed. 
33 
It  can  also  be  mounted  with  a  spring  and  micrometer  screw,  like 
Jackson's  micrometer.  In  our  micrometer  the  lines  appear  to  stand 
out  in  relief,  and  are  jet  black,  while  the  spaces  between  them  are 
translucent  enough  to  admit  of  the  accurate  measurement  of  the  de- 
tails of  minute  algae  and  fungi  to  the  2  §iuv  °^  an  incn- 
Regarding  the  goniometer  : — 
1st.  A  circle  about  eighteen  inches  in  diameter  is  drawn  with 
India  ink,  divided  into  degrees.  The  centre  is  indicated  by  a  dot, 
and  one  diameter  is  drawn.  Every  five  and  ten  degrees  are  indicated 
by  longer  lines  than  those  indicating  single  degrees.  Every  ten  de- 
grees of  each  quadrant  are  numbered  from  0  to  90. 
2d.  A  negative  two  inches  in  diameter  is  taken  by  the  process 
referred  to  above,  and  from  this  a  transparent  positive  is  taken  on  a 
circle  of  micrometer  glass  cut  to  fit  the  tube  of  the  microscope.  It 
is  covered  with  a  circle  of  thin  glass  cemented  with  balsam,  and 
mounted  to  fit  the  tube  at  the  focal  point  of  a  positive  eye-piece.  A 
cobweb  is  drawn  across  the  diameter  of  the  lower  lens.  When  a  crys- 
tal is  to  be  measured,  the  stage  is  moved  till  the  apex  of  the  angle 
coincides  with  the  centre  of  the  goniometer  and  the  diameter  with  one 
side.  The  eye-piece  is  now  turned  till  the  cobweb  crossing  the  diam- 
eter at  the  centre  coincides  with  the  other  side  of  the  angle.  Now 
the  number  of  degrees  of  the  angle  can  be  read  at  the  circumference 
The  advantage  of  this  over  the  ordinary  microscope  goniometers  is 
that  in  ours  the  angles  of  the  crystal  and  the  degrees  of  the  gonio- 
meter are  on  the  same  line  of  sight  within  the  tube  of  the  microscope, 
while  in  the  ordinary  goniometer  the  degrees  are  marked  outside  the 
tube.  The  photographic  processes  by  which  the  above  are  made  can 
be  learned  by  consulting  any  of  the  standard  works  on  photography, 
under  the  sections  that  treat  of  copying  engravings  and  taking  trans- 
parent positives. — Amer.  Journ.  Sci.  and  Arts,  Dec,  1871. 
PRACTICAL  OBSERVATIONS  ON  ESSENTIAL  OIL  OF  MUSTARD 
SEED. 
By  Dr.  F.  A.  FlUckiger. 
The  contents  of  this  essay  may  be  resumed  as  follows : — When  to 
^he  essential  oil  of  mustard  seed  3  parts  of  concentrated  sulphuric 
acid  are  slowly  and  gradually  added,  care  being  taken  to  cool  the 
mixture,  sulphurous  acid  and  sulphocarbonic  oxide  are  evolved  after 
3 
