^DecembeVr?9T'}  ^^^^^'3^  ^^^^^^         LemOU   OH.  561 
alcohol  was  found  satisfactory.  Each  cubic  centimetre  then  ap- 
proximates I  mgm.  of  Citral.  (loo  to  130  mgms.  in  50  c.c.  may  be 
used  and  smaller  aliquot  portions  taken  for  the  test.) 
Ninety-five  per  cent,  alcohol  without  previous  purification  was 
used  in  all  the  operations  herein  recorded.  A  i  per  cent,  solution  of 
metaphenylene  diamine  hydrochloride  in  diluted  alcohol  was  em- 
ployed as  reagent.  This  solution  was  shaken  with,  and  filtered 
through  bone  black  before  using. 
About  1.5  c.c.  of  oil  of  lemon  is  measured  into  a  50  c.c.  weighed 
flask,  accurately  weighed,  and  made  up  to  the  mark  with  95  per 
cent,  alcohol,  stoppered  and  thoroughly  shaken.  From  two  to  four 
c.c.  of  this  solution  are  then  accurately  measured  from  a  pipette 
calibrated  to  i/ioo  c.c.  into  a  Nessler  tube,  10  c.c.  of  the  filtered 
solution  of  metaphenylene  diamine  hydrochloride  added,  and  the 
volume  made  up  to  the  25  c.c.  mark  on  the  tube,  with  alcohol.  The 
same  or  a  corresponding  amount  of  standard  Citral  solution  is  then 
pipetted  into  another  tube  and  treated  in  the  same  way.  The  solu- 
tions after  shaking  are  compared  by  viewing  them  transversely 
and  the  stronger  one  is  diluted  with  95  per  cent,  alcohol  until  the 
reddish-yellow  colors  appear  to  be  identical.  The  volumes  are  then 
measured  and  the  subsequent  calculations  are  based  on  the  amount 
of  Citral  present  in  the  standard.  If  these  volumes  vary  more  than 
4  c.c,  one  from  the  other,  the  test  should  be  repeated  using  a  rela- 
tively smaller  amount  of  the  stronger  solution.  We  have  found  it 
advisable  to  compare  the  colors  of  the  solutions  when  approximately 
3  to  5  mgms.  of  Citral  are  present  in  the  standard.  Two  or  three 
close  readings,  all  of  them  made  in  volumes  of  approximately  25 
c.c,  should  be  obtained. 
The  method  of  calculating  the  results  is  comparatively  simple. 
Taking  as  complex  a  case  as  possible: 
Assume  that  each  c.c.  of  the  standard  contains  1.2  mg.  of  Citral, 
and  that  there  are  1.30  grams  of  lemon  oil  in  50  c.c  of  an  alcoholic 
solution.  Then,  if  3  cc.  of  the  standard  and  3.2  c.c.  of  the  solution 
of  oil  of  lemon  are  used  in  the  test — and  if  the  iinai  volume  of  the 
standard  is  26  c.c  (after  colorimetric  comparison  and  dilution)  and 
provided  the  other  solution  measures  25  c.c. — 
Each  cc  of  the  diluted  standard  is  equivalent  to  each  c.c.  of  the 
T.2  X  3 
other  solution,  and  contains  '    mgs.  of  Citral. 
26 
The  total  final  volume  of  the  unknown  (oil  of  lemon)  sohition 
