356  WEIGHING  OF  MOIST  PRECIPITATES. 
by  Pereira  carrageenin,  it  appears  to  differ  chiefly  in  its  power 
of  combining  with  a  great  amount  of  water  to  form  a  jelly, 
which  is  not  the  case  with  carrageenin. 
Of  the  botanical  origin  of  crude  gelose  or  Japanese  isinglass 
and  the  mode  of  its  preparation  in  Japan  and  China  we  are  not 
well  informed.  M.  Payen  finds  it  may  be  extracted  from  many 
species  of  sea-weed,  but  especially  from  Gelidium  corneum  La- 
mour.  and  G-racilaria  lichenoides  Grev.,  the  former  of  which 
yielded  in  his  experiments  to  the  extent  of  27  per  cent.  Gelidi- 
um corneum  is  certainly  used  by  the  Chinese  as  I  find  by  a  small 
collection  of  economic  Chinese  algce  sent  to  the  Society  of  Arts 
in  1857,f  the  specimens  in  which  Dr.  Harvey  of  Dublin  has  at 
my  request  been  kind  enough  to  examine  and  name.  It  appears 
however  that  several  other  sea-weeds  are  likewise  employed  by 
the  Chinese,  some  of  them  on  account  of  their  gelatinous  quali- 
ties ;  such  are  Laurencia  papillosa  Grev.,  Laminaria  saccharina 
Lamour.,  Porphyra  vulgaris  Ag.,  and  a  species  of  Gracilaria, 
apparently  G.  crassa  Harv.  (Alg.  Zeylan.  No.  29.)  Another 
sea-weed  which  is  largely  collected  in  the  Indian  archipelago  for 
exportation  to  China,  and  which  is  one  of  the  species  known  as 
Agar-agar  is  Eucheuma  spinosa  Ag. —  London  Pharm.  Jour, 
April,  1860. 
WEIGHING  OF  MOIST  PRECIPITATES. 
By  Ferdinand  F.  Mater. 
Mr.  Ch.  Mene,  of  Creusot,  (Journ.  de  Pharm.  et  de  Chemie, 
Oct.  1858,)  gives  a  mode  of  weighing  which  does  away  to  a 
great  extent  with  the  tediousness  and  difficulties  attending  the 
drying  of  many  precipitates,  especially  in  volumetric  analysis. 
He  washes  the  precipitate  thoroughly  by  decantation,  and  then 
introduces  it  carefully  into  a  bottle,  the  exact  weight  of  which, 
when  filled  with  distilled  water  at  a  certain  temperature,  is  known. 
Since  the  precipitate  is  heavier  than  water,  the  bottle  when 
filled  again  will  weighs  more  than  without  the  precipitate,  and 
the  difference  between  the  two  weights  furnishes  the  means 
of  calculating  the  weight  of  the  precipitate. 
tJourn.  of  the  Society  of  Arts,  30th  Oct.,  1857,  and  24th  Feb.,  1860. 
