[*'m-}  International  Congresses.  373 
A  similar  method  was  employed  with  the  oils,  the  results  of 
which  are  shown  below. 
TABLE  VI. 
Substance. 
Number. 
Rotation 
Observed. 
Rotation 
Calculated. 
Per  Cent,  of 
Deviation. 
Orange  oil. 
1 
86°-9i 
Nutmeg  oil. 
2 
2I°'58 
Mixture  of  i  and  2. 
53°77 
54°  '24 
0-9 
Turpentine. 
3 
i2o-34 
Mint. 
4 
-34°  75 
Mixture  of  4  and  5. 
-I5°-82 
-i5°7i 
o'3 
Mixture  of  r,  2,  4,  5. 
I9O-02 
i8°-97 
0-3 
The  results  of  the  experiments  described  in  this  paper  indicate 
that  in  making  saccharimetric  determinations  various  substances 
contained  in  tubes  placed  end  to  end  yield  results  which  are  equal 
to  the  sum  of  the  results  taken  separately,  and  furthermore,  sub- 
stances physically  mixed  together  preserve  their  optical  rotating 
properties  independently  of  each  other.  This  last  law  would 
enable  one  to  determine  the  proportions  of  a  mixture,  if  the  amount 
of  one  substance  and  the  rotating  properties  of  each  were  known. 
Incidentally  it  was  found  that  this  method  could  be  used  in  deter- 
mining the  length  of  a  column  of  liquid  with  greater  accuracy  than 
is  afforded  by  the  common  methods  of  measurement.  This  was 
illustrated  in  measuring  the  lengths  of  the  components  of  the 
double  tube. 
The  principal  sources  of  error  encountered  consisted  in  errors  of 
observation,  which  were  fairly  well  eliminated  by  repeated  trials, 
and  temperature  changes.  The  latter  were  undoubtedly  of  very 
little  moment. 
THE  INTERNATIONAL  PHARMACEUTICAL 
CONGRESSES. 
By  Fr.  Hoffmann. 
{Continued  from  page  325. ) 
FOURTH  CONGRESS    IN  ST.  PETERSBURG,  1 874. 
Early  in  1874  the  committee  appointed  by  the  Congress  in 
Vienna  addressed  a  circular  letter  of  invitation  and  a  programme 
for  the  fourth  International  Congress,  to  be  held  in  St.  Petersburg 
in  August;  1874.    The  invitation  was  extended  to  all  recognized 
