oSobeTi9^2^»""  }        Estimaiion  of  Methyl  Alcohol.  727 
to  within  0.2  per  cent,  the  percentage  of  methyl  alcohol  in  acetone 
when  the  former  varies  between  4  and  20  per  cent,  (above  the  latter 
limit  no  experiments  were  carried  out).  When  the  percentage  is 
below  the  former  limit  it  can  be  determined  approximately  by  com- 
paring the  color  reactions  with  those  produced  by  acetone  containing 
known  amounts  of  methyl  alcohol  and  when  the  experiments  are 
carried  out  under  the  same  conditions. 
As  an  alternative  method,  when  results  accurate  to  within  0.2 
per  cent,  can  be  obtained,  the  acetone  mixture  containing  the  lower 
percentage  of  methyl  alcohol  can  be  mixed  with  one  containing  a 
known  higher  percentage,  so  as  to  being  the  total  in  the  mixture 
to  more  than  4  per  cent.,  and  then  carrying  out  the  estimation  of  the 
methyl  alcohol  in  this  mixture  by  the  method  described  in  detail 
below,  subsequently  deducting  the  amount  of  added  methyl  alcohol 
from  the  result.  A  convenient  method  of  carrying  out  the  process 
is  to  add  to  the  acetone-methyl  alcohol  mixture  (containing  the 
unknown  amount  of  methyl  alcohol)  an  equal  volume  of  acetone 
containing  10  per  cent,  (by  volume,  as  the  specific  gravities  of 
methyl  alcohol  and  acetone  differ  only  very  slightly)  of  methyl 
alcohol.  By  subtracting  5  from  the  percentage  found  in  this  mix- 
ture, and  doubling  the  number  thus  obtained,  the  percentage  of 
methyl  alcohol  in  the  mixture  under  investigation  can  be  calculated. 
The  actual  determination  was  carried  out  in  the  following  man- 
ner: 5  Cc.  of  the  acetone  containing  methyl  alcohol  under  inves- 
tigation were  diluted  to  250  Cc.  with  water.  Quantities  each  of 
5  Cc.  of  this  mixture  were  introduced  into  a  series  of  test-tubes 
(6"  X  ^/\")  containing  5  Cc.  of  ammonium  persulphate  solutions 
of  varying  concentrations. 
Tablb  II. 
Formaldehyde  Reaction  after  Heating  with  Persulphate  Solutions  of 
Per  Cent.  MeOH 
in  Methyl  Alcohol 
the  Following  Concentrations. 
Acetone  Mixture. 
5  Per  Cent. 
4  Per  Cent. 
3  Per  Cent. 
2  Per  Cent. 
1  Per  Cent. 
10 
0 
? 
+  +  + 
+  +  +  +  + 
+  +  +  +  + 
9 
0 
? 
+  +  + 
+  +  +  +  + 
+  +  +  +  + 
8 
0 
0 
+  +  + 
+  +  +  +  + 
7 
0 
0 
? 
+  +  + 
+  +  +  +  + 
6 
0 
0 
0 
+  +  +  +  + 
5 
0 
0 
0 
+  +  +  + 
4 
0 
0 
0 
? 
+  +  + 
3 
0 
0 
0 
0 
+  +  + 
2 
0 
0 
0 
0 
I 
0 
0 
0 
0 
? 
