DRYING  OF  OILS  BY  METALLIC  SALTS.  265 
A  very  important  fact  which  has  arisen  from  our  experiments 
is.  that  if  the  internal  motion  shall  manifest  itself  in  a  distinct 
manner,  a  medium  temperature  from  50°  to  59°  Fahr.  must  ex- 
ist, while  under  this  degree  of  heat  to  32°  the  action  of  the  in- 
citing or  promoting  body  is  always  weaker.  The  necessity  of  a 
moderate  temperature  points  out  the  analogy  of  this  phenomenon 
to  fermentation.  We  may  remark  here  that  the  increase  of 
weight  of  a  layer  on  tin,  after  it  was  completely  dry,  amounted 
to  16  per  cent,  of  the  weight  of  the  oil  employed. 
Farther,  our  experiments  have  shown  that  the  direct  or  re- 
flected light  of  the  sun  had  a  remarkable  influence  on  the  phe* 
nomena  accompanying  the  drying  of  the  oil.  Thus,  a  surface  of 
tin  on  which  a  film  was  painted,  consisting  of  69  grammes  of  oil 
boiled  with  black  oxide  of  manganese  and  zinc-white,  had  taken 
up,  after  seven  hours,  in  a  dark  place,  only  about  1.1  gramme ; 
after  twenty-four  hours,  the  increase  amounted  to  2.23  grammes  ; 
while  a  similar  surface  exposed  in  a  laboratory,  at  the  same  tem- 
perature, to  the  light  of  the  bright  sky,  had  taken  up  in  seven 
hours  about  3.33  grammes,  and  after  twenty-four  hours  about 
4.42  grammes.  Under  the  direct  influence  of  sunlight,  the  ab- 
sorption is  still  more  rapid  than  in  the  foregoing  cases.  In  an 
experiment  of  twenty-four  hours'  duration,  a  similar  surface 
covered  with  35  grammes  of  zinc- white  paint,  with  drying  ingre- 
dients, had  taken  up  about  4  grammes,  and  evolved  .345  gram, 
mes  of  water,  and  1  gramme  of  carbonic  acid.  The  water  ob- 
tained appeared  to  arise  from  the  entire  surface  of  the  glass 
vessel  employed  for  the  experiment,  and  according  to  various 
weighings  it  was  not  proportional  to  the  evolved  carbonic  acid. 
From  the  above,  it  seems  that  the  absorption  of  the  oxygen  by 
drying  oils,  under  the  influence  of  light  and  heat,  is  the  conse- 
quence of  an  internal  impulse,  which  acts  in  the  way  of  a 
ferment. 
These,  our  new  views,  were  established  by  a  large  number  of 
facts,  for  we  found  bodies  which,  under  the  influence  of  light 
and  a  moderate  temperature,  in  extremely  small  quantities,  and 
in  a  very  short  time,  effected  the  drying  of  the  oil,  or  rather  con- 
verted it  into  resin,  by  which  carbonic  acid  was  evolved  and  the 
oxygen  of  the  air  assimilated.  There  is,  therefore,  in  our  opin- 
ion, an  oil  fermentation  analogous  to  the  lactic  acid  fermentation. 
