624  Properties  and  Uses  of  Formaldehyde.  { A^ovSer !vSt 
(1)  The  solution  may  be  directly  titrated  with  standard  solution 
of  ammonia,  rosolic  acid  being  used  to  indicate  the  complete  con- 
version of  the  formaldehyde  into  hexamethyleneamine. 
(2)  Excess  of  standard  ammonia  having  been  added,  the  solution 
may  be  titrated  back  again  with  standard  acid. 
(3)  The  solution  may  be  evaporated  to  dryness  with  excess  of 
standard  ammonia  and  the  hexamethyleneamine  weighed,  the  for- 
maldehyde being  calculated  from  the  following  equation  : 
6CH20  +  4NH3  =  (CH2)6N4  -f  6H20. 
(4)  The  solution  containing  formaldehyde  may  be  heated  for 
several  days  in  a  closed  vescel  on  a  water-bath  with  excess  of  sodium 
hydrate ;  sodium  formate  and  methyl  alcohol  are  produced,  and  the 
excess  of  sodium  hydrate  is  determined  by  titration  with  acid 
(Allen). 
(5)  The  insolubility  of  the  precipitate  formed  by  sulphuric  acid, 
phenol  and  formaldehyde  in  the  phenol-sulphuric  test  has  led  O. 
Hehner  to  suggest  its  utilization  for  the  determination  of  formalde- 
hyde in  dilute  solutions.  It  must  be  borne  in  mind  that  the  whole  of 
the  formaldehyde  cannot  be  separated  by  distillation,  even  when  three- 
fourths  of  the  volume  of  the  liquid  containing  it  has  been  collected 
as  distillate ;  the  first  four  of  the  foregoing  methods,  therefore,  if 
accurate  results  be  desired,  are  only  applicable  to  solutions  in  which 
no  other  interfering  constituent  exists.  Some  other  way  of  remov- 
ing the  formaldehyde  is  apparently  necessary  for  its  exact  quanti- 
tative determination  in  complex  mixtures. 
ECONOMIC  APPLICATIONS  OF  FORMALDEHYDE. 
Formaldehyde,  as  shown  by  Slater  and  Rideal,  when  employed 
of  such  a  strength  in  weak  alcoholic  liquids  as  to  be  fatal  to  lactic 
and  butyric  acid  organisms  and  other  bacteria  which  produce 
injurious  secondary  fermentation,  does  not  interfere  with  the  growth 
of  the  yeast  plant,  nor  does  it  hinder  in  any  way  the  formation  of 
alcohol.  This  fact  has  been  turned  to  account  in  the  brewing 
industry  for  producing  pure  cultivations  of  yeast,  and  preventing 
souring,  cloudiness,  or  ropiness  in  the  finished  product ;  it  should 
also  prove  equally  useful  in  ensuring  soundness  in  such  fermented 
liquids  as  orange  and  ginger  wines,  perry,  cider,  etc.  The  propor- 
tion necessary  is  from  1  in  10,000  to  1  in  20,000. 
