ON  THE  MATERIALS  USED  FOR  CLOTHES. 
369 
following  considerations  have  sufficiently  proved  the  correctness 
of  this  distinction  :  1st.  Hygrometric  water  may  be  absorbed  in 
considerable  quantities  without  modifying  the  principal  physical 
properties  of  the  fabric ;  it  can  be  discovered  only  with  the 
balance.  Water  of  interposition,  on  the  contrary,  powerfully 
modifies  these  same  properties,  and  may  be  perceived  by  the 
touch.  2nd.  Hygrometric  water  can  only  be  removed  by  pres- 
sure ;  its  weight  will  not  cause  it  to  descend  into  the  lower  por- 
tions of  the  stuff;  this  effect  will  be  produced  with  water  of 
interposition.  3rd.  Water  of  interposition  will  always  evapor- 
ate completely  when  the  material  is  placed  in  an  atmosphere 
which  is  not  saturated  with  vapor.  Hygrometric  water,  on  the 
contrary,  only  evaporates  entirely  in  a  perfectly  dry  medium. 
Its  weight  varies  with  the  hygrometric  state  of  the  surrounding 
atmosphere  and  the  temperature  of  the  fabric. 
To  estimate  the  hygrometric  water  and  the  water  of  inter- 
position, the  fabric  must  be  weighed  after  being  twenty-four 
hours  over  quick  lime,  and  then  over  water ;  the  material  being 
put  into  the  bell-glass,  either  dry,  or  saturated  with  water  by 
having  been  steeped  in  it  for  some  time.  The  difference  of  the 
weight  will  at  once  furnish  the  desired  results.  The  average 
quantities  of  hygrometric  water  absorbed  have  been  as  follows : 
cotton,  0.10  of  the  weight  of  the  fabrics  ;  linen,  0-15  ;  wool,  0-18 
to  0-20.  For  water  of  interposition  I  obtained  the  numbers  : 
linen,  0-5 ;  cotton,  0-8  to  0-9 ;  wool,  1*5. 
I  have  ascertained  that  when  a  fabric  removes  as  hygrometric 
water  the  liquid  which  moistens  any  surface  with  which  it  is  in 
contact,  the  temperature  of  the  latter  does  not  vary.  The  water 
passes  off,  it  is  true,  in  the  gaseous  state ;  but,  by  condensing  im- 
mediately in  the  pores  of  the  fabric,  it  restores  the  heat  absorbed 
to  the  latent  state. 
The  conclusions  which  I  have  drawn  from  my  investigations 
are  as  follows  : — 
1.  — The  color  of  the  dress  has  no  sensible  influence  on  the 
loss  of  heat. 
2.  — All  fabrics  are  capable  of  absorbing  in  the  latent  state  a 
certain  quantity  of  hygrometric  water  ;  this  quantity,  which 
is  very  considerable  with  wool,  is  less  with  linen  and  especially 
with  cotton. 
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