AmbicUr*i^iarm' }   Lactometer  and  Fat  in  Milk  Control.  823 
A  rule  so  simple  is  easily  remembered,  and  applied  without 
written  calculations :  Add  3  to  the  lactometer  reading  and  then 
divide  by  10.  The  result  is  the  minimum  percentage  of  fat  in  a 
mixed  milk  above  suspicion  of  being  skimmed. 
This  rule  has  its  limitations.  One  limit  to  its  use  as  a  guide 
in  sorting  out  milks  that  merit  detailed  examination  can  readily  be 
shown  when  the  line  representing  the  minimum  legal  standards  in 
Pennsylvania  11  is  plotted  on  the  same  axes  with  it.  To  obtain  the 
values  necessary  for  plotting  this  line,  equation  (1)  may  be  trans- 
formed as  follows : 
x  =  y4L  +  %  =  i2% 
whence, 
F  —  10  —  0.20833  L  ,   (13) 
The  values  in  the  following  table  have  been  calculated  by  use  of 
this  equation  (13)  : 
TABLE  II. 
%fat 
Lactometer 
calculated  by 
reading  at  6o° 
formula  (15) 
27 
44 
28 
4.2 
29 
4.0 
30 
37 
31 
3-5 
32 
3-3 
33 
3-i 
Any  of  these  calculated  values  of  F  is  the  least  or  minimum  fat 
percentage  to  be  expected  in  a  (legal)  standard  mixed  milk  that 
has  exhibited  the  corresponding  lactometer  reading.  As  an  exam- 
ple, consider  a  mixed  milk  found  to  have  a  lactometer  reading  of 
31.  The  minimum  fat  per  cent,  in  such  a  milk  if  it  is  above  (legal) 
standard,  i.  e.,  if  it  contains  not  less  than  12  per  cent,  of  total  solids, 
is  3-5  Per  cent-  Should  this  milk  upon  analysis  show  less  than 
3.5  per  cent,  fat,  it  should  be  set  aside  for  further  consideration 
because  it  is  not  above  suspicion  of  being  sub-standard. 
When  the  numerical  values  in  Table  I  and  II  are  plotted  on 
the  same  axes,  the  lines  marked  I  and  II  respectively  on  Fig.  I  are 
11  See  footnote  No.  1. 
