92  Testing  of  Formaldehyde.  {^f^lxyMl^ 
rapidly  when  exposed  to  diffused  sunlight  than  in  the  dark.  Spe- 
cific  gravity,  1-109  at  —J  free  acid,  assumed  to  be  formic  acid, 
017  per  cent.  Residue  on  ignition,  019  per  cent.,  consisting  of 
sodium  chloride  and  a  little  sodium  carbonate. 
Per  Cent. 
Strength,  by  ammonia  method   37*4,37*5 
"  fixed-alkali    "    37*3,  37'6 
"  hydroxylamine  method  37*2,  37*3 
Sample  II. — Color  faintly  yellowish  ;  contains  fine  particles  of 
extraneous  matter,  but  is  free  from  a  deposit  of  para-formaldehyde. 
Specific  gravity,  1-052  at  _1_  ;  free  acid,  0-065  per  cent.  ;  traces  of 
acetone  ;  residue  on  ignition,  0-015  per  cent.,  consisting  of  copper 
oxide. 
Per  Cent. 
Strength,  by  ammonia  method   34  6,  34-7 
"  fixed  alkali    "   35-3,  34-7,  35-6,  34-0 
"  hydroxylamine  method  34'4,  34*6 
Cause  of  discrepant  results  by  the  fixed-alkali  method  unknown. 
This  solution  is  claimed  to  be  40  per  cent,  strong  on  the  label. 
Sample  III. — Clear,  faintly  yellowish;  specific  gravity,  1-057  at 
I  r  0 
free  acid,  007  per  cent.;  traces  of  acetone;  residue  on  igni- 
tion, 0  032  per  cent.,  consisting  of  copper  oxide. 
Per  Cent. 
Strength,  by  ammonia  method  (modified)   35*3,  35  *2 
"  fixed  alkali    "   35 '3,  35*2 
"  hydroxylamine  method  35 'o,  35  "i 
Samples  II  and  III  are  apparently  made  directly  from  woodspirit, 
as  judged  by  the  presence  of  acetone,  copper,  and  by  the  dispropor- 
tionately lower  specific  gravity,  indicating  presence  of  a  lighter 
liquid,  probably  methyl  alcohol.  These  samples  also  have  more 
empyreuma  than  is  the  case  with  Sample  I ;  they  leave  a  smaller 
residue  of  para-formaldehyde  when  evaporated  spontaneously  and 
deposit  no  para-formaldehyde  when  exposed  to  daylight  for  nearly 
a  month. 
TESTS  OF  IDENTITY  AND  PURITY. 
The  following  list  of  tests  is  presented  as  a  convenience  to  those 
who  may  wish  to  avail  themselves  of  it  as  a  guide  in  the  examina- 
tion of  commercial  products.    The  details  of  the  tests  are  arranged 
