Am.  Jour.  Pharm. 
Dec,  1921. 
£   Lactometer  and  Fat  in  Milk  Control. 
827 
N  =  A  +  dB  +  d2C  +  d3C  +  d4E  +  . . .  .  
where  N  =  the  normality  of  the  sulphuric  acid 
d  =  the  specific  gravity  D15°c- 
A  =  — 297.800 
B  =  +916.349 
C  =  —1047.430 
D  =  +506.431 
E  =  —77.5467 
It  it  better  to  use  a  six-place  logarithm  table  in  applying  this 
approximate  formula. 
For  more  general  use,  cane  sugar  is  suggested,  because  in  the 
form  of  the  best  grades  of  granulated  sugar  it  is  easily  obtainable 
and  is  cheap.  A  solution  of  any  desired  percentage  can  readily  be 
made  by  weighing  off  the  proper  quantities  of  sugar  and  water. 
In  Table  IV  are  given  the  proper  normalities  of  sulphuric  acid 
and  the  proper  percentages  of  sugar  for  obtaining  solutions  for  use 
in  calibrating,  such  that  they  will  have  specific  gravities  located  at 
every  five  degrees  along  the  Quevenne  scale.  The  normalities  of 
the  sulphuric  acid  were  arrived  at  by  application  of  the  approxima- 
tion formula  already  given,  after  deriving  it  from  the  table  to  be 
found  in  Landoldt,  Bornstein,  Meyerhoffer  Phys.  Chem.  Tabellen, 
page  326.  The  percentage  of  the  sugar  solutions  were  worked  out 
from  the  same  source,  page  364,  checked  by  values  in  Tables  An- 
nualles  Internationales  de  Constantes  et  Donees  Numeriques,  page 
17.  In  all  of  these  operations  due  attention  was  given  to  the  fact 
that  the  tables  give  densities  that  are  not  on  the  same  temperature 
basis  as  the  densities  of  milk  (otherwise  table  10,  p.  389,  Methods 
of  Analysis  Of.  Agr.  Chemists,  1919,  could  be  used).  After  sugar 
solutions  have  been  made,  if  there  is  any  doubt  about  them  they  may 
of  course  be  checked  by  the  polarimeter  or  by  the  refractometer. 
TABLE  IV. 
Specific 
gravity  at  15°  C. 
Lactometer 
reading 
Normality  of 
sulphuric  acid 
Percentage  of 
sugar  solution 
I.0200 
I.0250 
I.0300 
I.0350 
I.0400 
25 
30 
35 
40 
0.618 
0.771 
0.929 
1.087 
1.240 
5-065 
6.307 
7-  537 
8-  755 
9-  963 
