^Q2         Colorimetric  Determination  of  Mediums.    !AnV  -Touf-  Pha0rm- 
Oy^  J  l     August,  19 18. 
of  the  extreme  purity  of  the  salt.  Control  analyses  of  the  current 
product  show  a  96  per  cent,  grade,  with  less  than  0.4  per  cent,  of 
sulphates,  the  remaining  impurity  being  principally  sodium  chloride. 
The  acetone  and  ketones  produced  by  retorting  the  acetate  salts  are 
being  used  almost  entirely  in  the  manufacture  of  smokeless  powder 
and  aeroplane  dopes  under  British  contracts,  thus  releasing  an 
equivalent  amount  of  acetate  of  lime  for  industrial  users.  The  sol- 
vents produced  from  the  propionate  and  butyrate  salts  are  some- 
thing new  in  the  solvent  field,  and  by  superseding  amyl  acetate,  etc., 
in  many  directions,  will  still  further  ease  the  present  acetate  of  lime 
shortage. 
COLORIMETRIC  DETERMINATION  OF  REACTION  OF 
BACTERIOLOGIC  MEDIUMS  AND  OTHER  FLUIDS.1 
By  George  D.  Barnett,  M.D.. 
Passed  Assistant  Surgeon,  U.  S.  Naval  Reserve  Force, 
AND 
Herbert  S.  Chapman,  M.D., 
Assistant  Surgeon,  U.  S.  Navy,  San  Francisco. 
The  colorimetric  methods  in  common  use  for  determining  and 
adjusting  the  reaction  of  bacteriologic  mediums  and  other  fluids 
involve  the  use  of  standard  solutions  of  known  hydrogen  ion  con- 
centration. A  variety  of  such  solutions  has  been  described,  and 
they  are  readily  prepared  by  any  one  having  a  moderate  chemical 
equipment  and  ability.  Just  now,  however,  many  men  with  com- 
paratively little  chemical  training  are  confronted  with  problems  of 
this  nature,  and  the  method  here  described  has  therefore  been  de- 
vised to  accomplish  a  fairly  accurate  determination  of  hydrogen  ion 
concentration  without  the  necessity  of  preparing  standard  solutions 
or  of  depending  on  those  prepared  by  others.  We  are  here  con- 
cerned only  with  reactions  lying  between  7.0  and  8.0,  and  only 
phenolsulphonephthalein  has  been  used  as  an  indicator.  Other  in- 
dicators and  other  ranges  of  acidity  will  be  investigated  later. 
In  this  method  use  is  made  of  the  principle  of  superimposing 
the  two  extreme  colors  of  the  indicator,  as  used  by  Clark  and  Lubs,2 
1  From  the  Journal  of  the  American  Aledical  Association,  April  13,  1918. 
2  Clark  and  Lubs.  Jour.  BacterioL,  1917,  2,  109,  191. 
