194       QUANTITATIVE  DETERMINATION   01'  TANNIN,  ETC. 
too  thick  to  use  conveniently,  a  solution  of  half  the  strength  was 
used,  which  was  better  adapted  to  the  purpose.  Most  of  the 
gelatin  to  be  obtained  not  being  pure,  it  was  found  necessary 
to  determine  the  strength  of  each  solution  of  gelatin  employed  ; 
this  was  done  by  determining  the  number  of  cubic  centimetres 
of  each  solution  that  were  required  to  precipitate  10  grains  of 
pure  tannin  ;  and  this  then  tak  en  as  the  standard — instead  of 
the  amount  of  gelatin  employed  in  making  the  solution.  In 
determining  the  amount  of  tannin  in  the  following  substances, 
100  grains  were  treated  by  the  above  process  three  successive 
times,  and  the  average  of  the  three  results  taken  as  the  amount 
of  tannin  that  each  sample  of  the  substance  contains.  The 
determination  effected  in  the  way  above  described  produced 
results  as  follows  : 
Percent. 
Alum  root  (Heuchera  americana),  1st  sample,          .         .  20*40 
2d       "              .          .  18-50 
Blackberry  root  (Bubus  villosus),         .         ,         .          .  9"75 
Trailing  arbutus  (Epigsea  repens),        ....  3*50 
Kino  (Pterocarpus  marsupium),  1st  sample,    .         .          .  57"61 
2d               .         .          .  39-18 
Grreen  tea  (Thea  viridis),  ,       .         .         .         .         .  16*75 
Black    "  (TheaBohea),   13-25 
Dogwood  bark  (Gornus  Florida),          ....  3-00 
Yarrow  (Achillea  millefolium),           ....  4-15 
Hemlock  spruce  bark  (Abies  Canadensis),       .          .         .  7-13 
Witchhazel  bark  (Hamamelis  Yirgioiana),       .         .          .  8*10 
Marsh  rosemary  (Statice  caroliniana),  1st  sample,      .          .  18"06 
"           2d     "          .          .  14-43 
Rhatany  (Krameria  triandra),            ....  22*79 
Red  rose  (Rosa  Gallica),          .....  5-49 
Bistort  (Polygonum  bistorta),            .          .         .         .  21-00 
Best  galls  (ex  Quercus  infectoria),      .          .         .       '  .  80*07 
White  galls,  inferior  (ex  Quercus  infectoria),            .          .  30-72 
Good  commercial  powd.  galls  (ex  Quercus  infectoria),          .  52*39 
Common  agrimony  (Agrimonia  eupatoriaj,      .          .          .  4  75 
American  alder  (Alnus  serrulata)  bark,           .          .          .  4-00 
American  alder  (Alnus  serrulata),  aments,       .          .          .  1*50 
Black  birch  (Betula  lenta),       .....  3*30 
Catechu,  No.  1,            ......  49*40 
"        •»    2,  .         .                   ....  40*20 
"        "    3,  .         .                   .         .         .         .  32-80 
