Amjune,r'I8P7h9a^I^• }  Note  on  Plasma.  3 1 3 
difference  being  that  54*68  grains  of  the  latter  ingredient  are  ordered  to 
each  fluidounce  of  glycerin  instead  of  70,  as  in  the  former  case. 
Up  to  the  present  time  plasma,  or  glycerin  of  starch,  has  not,  I 
believe,  come  largely  into  use,  owing,  no  doubt,  in  some  measure, 
though  not  entirely,  to  its  tendency  to  soften  by  deliquescence,  as 
already  referred  to;  no  remedy,  that  I  am  aware  of,  having  as  yet  been 
effectually  applied  or  suggested.1  It  may  here  be  stated  that  it  is  to 
this  point  that  the  present  note  more  especially  refers. 
If  plasma  be  kept  in  an  air-tight  stoppered  bottle  it  will  retain  its 
firm  consistence  indefinitely.  It  owes  its  softening  property,  therefore, 
to  the  large  extent  to  which  the  glycerin  it  contains  is  capable  of  sub- 
tracting moisture  from  the  atmosphere,  the  starch  playing  no  part  what- 
ever in  the  change  thus  brought  about.  This  property  of  glycerin  is 
exercised  exactly  in  relation  to  the  two  following  conditions,  namely — 
the  amount  of  superincumbent  moisture,  and  the  extent  of  surface  that 
may  be  exposed  thereto.  The  behavior  of  glycerin  in  a  very  moist 
atmosphere  is  both  curious  and  interesting.  The  moisture  in  the  form 
of  water  collects  and  floats  on  its  surface,  and  taking  up  or  dissolving  a 
considerable  proportion  of  the  subjacent  glycerin  (probably  more  than 
half  its  own  weight),  attracts  more  moisture,  which,  in  turn,  exercises 
its  solvent  power  and  acquires  a  capability  of  still  further  absorption. 
Thus  the  action  goes  on,  not  necessarily,  as  may  be  thought,  in  a  con- 
stantly decreasing  ratio  as  the  water  increases  in  amount,  but  at  an 
almost  uniform  rate  from  week  to  week.  The  mixture  of  glycerin  and 
water  is  not  so  actively  hygrometric  as  the  glycerin  alone,  but  the  com- 
bination once  effected  the  action  continues  with  singular  uniformity. 
The  following  table  will  serve,  in  some  measure,  to  illustrate  this. 
Hygrometric  Action  of  Glycerin  in  Atmosphere  Charged  with  Excess  of 
Moisture. 
Increase  in  Weight. 
Surface  Area.                           ist  week.     2d  week.     3d  week.      4th  week.  Total  1  month. 
3-1416  square  inches,                56  grs.      44  grs.      48  grs.      47  grs.  195  grs. 
9-6211          "                       156          119          113          102  490 
28-2744          "                       504          341           310          315  1470 
It  will  be  seen  that  in  each  case  there  is  a  diminution  of  the  increase 
1The  glycerin  of  starch  of  the  German  Pharmacopoeia  is  a  step  in  this  direction, 
but  the  water  therein  contained  (about  1  in  12)  is  not  nearly  sufficient  to  rectify  the 
hygroscopic  character  of  the  resulting  mass. 
