820 
Lactometer  and  Fat  in  Milk  Control.    5  Am.  jour  Pharm. 
(      Dec,  1921. 
been  thus  expressed: 
GT 
m  - 
GT  —  (iooG-ioo) 
(2) 
The  numerical  value  of  m  ranges  from  1.2  to  14,  depending  upon 
the  ratio  obtaining  in  any  given  milk  between  the  fat  and  the  non- 
fatty  solids.  It  does  not  exceed  1.34  in  mixed  milks  beyond  sus- 
picion of  skimming.8  If  therefore  the  value  1.34  be  substituted  for 
m  in  equation  (2),  thus, 
an  equation  (3)  is  obtained  that  defines  the  minimum  values  of  G 
and  T  that  will  be  met  with  in  mixed  milks  which  may  in  routine 
examinations  be  passed  as  unskimmed. 
Formulae  that  serve  to  bring  out  probable  skimming  are  more 
generally  useful  in  routine  work  than  other  milk  formulae.  The 
writer's  experience  leads  to  the  conclusion  that  in  1920  in  the  subur- 
ban area  from  which  the  market  milk  samples  (upward  of  a  thou- 
sand) examined  by  him  were  drawn,  skimmed  milk  was  from,  thirty 
to  forty  times  as  common  as  watered  milk  or  as  sub-standard  milk. 
This  is  largely  due  to  the  fact  that  the  larger  dealers  practice 
skimming  in  one  form  or  another  under  the  name  standardization.9 
Therefore  the  first  and  most  important  step  in  developing  the  sort- 
ing method  herein  proposed  was  to  obtain  a  formula  involving  only 
the  lactometer  reading  L  and  the  fat  per  cent.  F,  by  which  milks 
suspicious  of  skimming  would  be  indicated. 
Such  an  equation  was  developed  algebraically  from  (1)  and 
(3).  In  the  development  it  is  necessary  to  make  use  of  the  fact 
that  the  lactometer  reading  L,  expressed  as  it  usually  is  in  degrees 
on  the  Quevenne  lactometer  scale,  bears  the  following  relation  to 
the  specific  gravity  G  of  the  milk  (provided  both  readings  are  at 
the  standard  temperature,  6o°  F.)  : 
GT 
(3) 
i-34  = 
GT  —  (100  G  —  100) 
L  —  1000G  —  1000, 
(4) 
whence, 
G  =  L  +  1000 
(5) 
1000 
8  See  Van  Slyke,  M odern  Methods  of  Testing  Milk  and  Milk  Products, 
1907,  p.  140;  and  Woodman,  Food  Analysis,  191 5,  p.  139. 
9  See  Parker,  City  Milk  Supply,  191 7,  p.  261. 
