Am.  Jour.  Pharm. ) 
October,  1904.  / 
Theory  of  Indicators,  etc. 
463 
is  entirely  indifferent  to  all  weak  organic  acids,  whether  of  the 
nature  of  aspartic  acid  or  the  stronger  types,  such  as  formic, 
acetic,  lactic,  etc.  This  indicator  is  of  great  value  in  differentiating 
the  weak  bases,  being  sensitive  not  only  to  ammonia,  but  also  to 
the  NH2  group  in  asparagin,  glycocol,  leucin,  tyrosin  and  such  com- 
pounds as  hydroxylamin,  but  indifferent  to  the  NH2  groups  of  the 
type  present  in  acetamid,  formamid  and  urea,  groups  that  are  asso- 
ciated directly  with  negative  CO. 
Meyer  and  other  investigators  have  made  the  assumption  that 
the  amido  acids  are  entirely  devoid  of  basic  characteristics.  These 
results,  however,  make  it  apparent  that  a  sharp  differentiation 
between  ammonia,  the  NH2  group  associated  with  carbon,  to  which 
hydrogen  is  attached,  and  the  NH2  group  associated  directly  with 
the  CO  group,  may  very  readily  be  effected. 
An  interesting  phase  of  this  work  is  shown  in  the  results  obtained 
rom  impure  tyrosin  and  asparagin.  In  both  these  cases  the  high 
nitrogen  content  indicated  the  probability  of  the  formation  of  some 
type  of  anhydride  through  internal  condensation.  This  result  was 
entirely  borne  out  by  the  figures  obtained  in  titration  after  the  sub- 
stance had  been  dissolved  in  water,  whereby  any  such  anhydride 
would  probably  be  decomposed.  Asa  result  the  end  point  obtained 
with  phloroglucinvanillin  drops  corresponded  exactly  with  the  dif- 
ference that  our  nitrogen  determination  had  led  us  to  expect.  The 
same  agreement  oi  errors  attributable  to  impurity  of  the  substance 
was  observed  to  a  modified  degree  in  leucin.  Not  having  methyl- 
amin  or  aethylamin  at  our  disposal  we  were  not  able  to  test  their 
behavior  towards  indicators  ;  but  from  the  literature  it  would  appear 
probable  that  bodies  of  this  type  would  exert,  just  as  does  ammonia, 
a  full  alkaline  effect  upon  alizarin,  and  possibly  even  on  phenol- 
phthalein.  Such  bodies  as  sethylendiamin,  having  two  NH2  groups, 
are  probably  mono-basic  to  phenolphthalein  and  di-basic  to  alizarin, 
but  this  question  will  be  referred  to  at  a  later  stage  in  discussing  the 
constitution  of  the  proteids. 
A  consideration  of  the  bearing  which  these  results  have  upon  the 
titrations  of  stomach  contents  and  the  constitution  of  the  proteids, 
will  be  reserved  until  the  action  of  the  indicators  here  employed  has 
been  studied  in  its  relationship  to  the  various  nitrogenous  products 
present  in  such  mixtures.  The  most  important  result  of  the  work 
recorded  in  this  section  is  the  means  which  it  affords  of  differentiat- 
