Am.  Jour.  Pharm.  i 
January,  1911.  j 
Note  on  Sulphur  Dioxide. 
19 
required  for  each  titration ;  whereas  in  the  residual  titration  process 
not  more  than  thirty  minutes  need  be  consumed  for  the  correspond- 
ing part  of  the  assay,  and  even  during  this  time  the  attention  of  the 
operator  is  not  required  as  closely  and  repeatedly  for  each  titration 
as  when  the  titration  is  carried  out  at  a  boiling  temperature,  and 
no  attention  at  all  is  required  from  the  operator  during  this  period 
when  the  mixture  is  simply  allowed  to  stand  at  ordinary  tempera- 
ture. It  would  seem,  therefore,  that  the  residual  titration  process 
has  many  advantages  over  the  method  in  which  the  titration  is  car- 
ried out  at  a  boiling  temperature,  which  should  justify  its  adoption 
in  the  next  revision  of  the  U.S. P.  And  since  practically  as  close 
results  are  obtained  by  simply  mixing  well  the  acid  with  about  twice 
the  amount  of  alkali  required  and  allowing  the  mixture  to  stand  from 
fifteen  to  thirty  minutes  before  titrating  the  excess  alkali,  as  when 
the  alkaline  mixture  is  boiled  for  fifteen  minutes,  it  would  seem  that 
'the  boiling  might  be  entirely  omitted,  and  the  assay  method  for 
lactic  acid  modified  to  read  somewhat  as  follows : 
To  about  two  grammes  of  the  sample  of  lactic  acid,  accurately 
weighed,  add  50  c.c.  of  normal  NaOH,  mix  well,  and  let  stand  for 
half  an  hour.  Then  titrate  the  excess  alkali  by  means  of  normal 
sulphuric  acid,  using  phenolphthalein  as  indicator.  The  number 
of  cubic  centimetres  of  the  alkali  found  to  be  required,  multiplied 
by  the  lactic  acid  equivalent  of  i  c.c.  (0.09  Gni.),  and  this  product 
divided  by  one-hundredth  of  the  weight  of  the  sample  taken  for  the 
assay,  will  express  in  percentage  the  lactic  acid  strength  of  the 
sample. 
A  NOTE  ON  THE  USE  OF  SULPHUR  DIOXIDE  IN  CHECK 
ING  THE  EQUIVALENCIES  OF  THE  VOLUMETRIC 
SOLUTIONS  OF  IODINE,  ALKALI,  AND  SILVER. 
By  Eli  as  Elvove. 
Hygienic  Laboratory,  U.   S.  Public  Health  and  Marine-Hospital  Service, 
Washington,  D.  C. 
In  connection  with  some  tests  which  are  being  carried  out  at 
the  Hygienic  Laboratoi-y  on  the  efficiency  of  a  sulphur  burning 
stove,  designed  by  Dr.  Norman  Roberts  and  Mr.  F.  A.  McDermott 
of  this  laboratory,  the  writer  has  had  occasion  to  estimate  the 
relative  amounts  of  SO^  and  SO;j  formed  in  these  combustions,  by 
