^""6cioher,  mT' }       ^ote  on  Assay  of  Formaldehyde.  465 
of  an  approximately  n/io  KCN  solution  and  the  flasks  tightly  stop- 
pered by  means  of  rubber  stoppers.  From  the  known  value  of  the 
formaldehyde  and  KCN  solutions  the  amount  of  KCN  added 
was  calculated  to  be  approximately  one-hundredth  of  an  equivalent 
in  excess  of  that  required  to  combine  with  all  of  the  formaldehyde 
present.  All  these  flasks  were  then  set  in  a'  large  water-bath,  the 
temperature  of  which  was  kept  at  about  40°  C,  and  allowed  to 
remain  in  this  bath  for  half  an  hour.  At  the  end  of  this  time,  the 
contents  of  flask  No.  i  was  added  to  a  mixture  of  5  c.c.  n/io 
AgNO^  and  20  c.c.  of  10  per  cent,  nitric  acid  in  a  200  c.c.  meas- 
uring flask  and  the  analysis  completed  as  in  the  former  experiments ; 
w^hile  flasks  Nos.  2,  3,  and  4  were  taken  out  of  this  bath  and  set 
in  another  large  water-bath,  which  was  kept  at  about  5°  C.  After 
remaining  in  this  bath  for  half  an  hour,  No.  2  was  treated  as  No.  i 
while  Nos.  3  and  4  were  taken  out  and  placed  again  in  the  bath  at 
40°  C.  After  this  second  warming  tO'  40°  C.  No.  3  was  treated  as 
were  Nos.  i  and  2,  while  No.  4  was  taken  out  of  this  bath  and  set 
again  in  the  bath  at  5°  C.  After  this  second  cooling  to  5°  C,  No.  4 
was  treated  as  those  preceding  it.  On  titrating  half  of  the  final 
filtrate  with  n/io  KCNS,  the  following  results  were  obtained : 
Found  equivalent  of  the 
25  c.c.  formaldehyde 
solution  in  c.c.  of 
N/io  AgNOs 
No.  I  required  1.45  c.c.  n/io  KCNS,  corresponding  to  30.59 
No.  2  2.03    "      "        "  "  "  31.75 
No.  3       "       1.48    "      "        "  "  "  30.65 
No.  4       "       2.01    "      "        "  "  "  31.71 
On  now  repeating  these  experiments  in  exactly  the  same  way 
except  that  the  excess  of  KCN  was  increased  to  approximately 
one-half  of  an  equivalent  (using  48  c.c.  of  n/io  KCN,  whose  fac- 
tor was  0.9875),  the  following  results  were  obtained: 
Found  equivalent  of  the 
25  c.c.  formaldehyde 
solution  in  c.c.  of 
N/io  AgNOs 
No.  I  required  2.42  c.c.  n/io  KCNS,  corresponding  to  32.24 
No.  2       "       2.50    "      "        "  "  "  32.40 
No.  3       "       2.35    "      "        "  "  "  32.10 
No.  4       "       2.50   "      "        "  "  "  32.40 
25  c.c.  of  the  foTmaldehyde  solution  used  were  found  equivalent  to 
32.4  c.c.  n/io  AgNOs,  while  33  c.c.  of  the  KCN  solution  were  found  equivalent 
to  32.69  c.c.  n/io  AgNO.i. 
^  The  amount  of  n/io  AgNOs  used  was  also  increased  to  20  c.c. 
