Am.  Jour.  Pharm.  ) 
April,  1921.  J 
Determination  of  Urea. 
265 
amalgam,  the  xanthone  is  transformed  into  xanthydrol: 
C6H4<CO>C0H4  +  H,  =  C8H4<CH0OH>C6H4 
Xanthydrol  in  the  presence  of  acid,  condenses  with  the  urea  to 
form  dixanthylurea  or  ureine: 
co^-^(c^),CH.OH.o]=^<ig;g|;j^jg+,H1 
^,        .       P  ,         .  .  .         dixanthylurea  420 
The  ration  of  the  molecular  weights  ==   —~? — =/. 
&  urea  00 
Xanthydrol  is  a  white  substance,  light,  inodorous,  and  insoluble 
in  water.  At  ordinary  temperature  1  gm.  dissolves  in  7  cc  methyl- 
alcohol,  and  in  10  cc  ethyl  alcohol.  Its  point  of  fusion  is  about 
i73°- 
In  order  to  operate  under  the  best  conditions,  the  precipitation 
should  be  made  in  solutions  containing  about  1  to  2  gm.  of  urea  per 
liter.  Use  10  cc  of  this  solution,  which  represents  from  10  to  20  mgr. 
of  urea.  From  70  to  140  mgr.  of  dixanthylurea  should  then  be 
weighed.  The  xanthydrol  should  be  employed  in  a  1  :io  methyl- 
alcoholic  solution. 
The  determination  of  urea  in  urine  is  carried  out  in  the  follow- 
ing manner : 
Take  10  cc  of  urine  diluted  to  100  cc,  add  35  cc  of  crystallizable 
(glacial)  acetic  acid;  add,  while  agitating,  1  cc  of  the  reagent;  con- 
tinue adding,  every  ten  minutes,  1  cc  of  the  reagent  until  5  cc  have 
been  added ;  set  aside  for  one  hour ;  collect  the  precipitate  of  dixan- 
thylurea on  a  small  tared  filter ;  after  draining,  wash  with  about  20  cc 
of  95  per  cent,  alcohol  added  in  small  portions;  dry  at  ioo°  and 
weigh.    The  weight,  divided  by  7,  represents  the  quantity  of  urea. 
The  following  substances  can  accompany  urea  in  the  urine 
without  forming  a  precipitate  with  xanthydrol  in  the  presence  of 
acetic  acid :  ammonia,  methyl  or  dimethylamine,  guanidine,  creatine, 
creatinine,  arginine,  glycocol,  hippuric  acid,  alanine,  leucine,  aspara- 
gine,  aspartic  acid,  glutamic  acid,  tyrosine,  uric  acid,  xanthine,  albu- 
minoids of  the  egg  and  of  the  blood,  fibrin,  gelatin,  peptone,  glycerin, 
erythrite,  mannite,  glucose,  levulose,  saccharose,  dextrin,  the  lactic 
acids,  tartaric  and  citric  acids.  Such  bodies  as  cyanamide,  dicyandi- 
amide,  and  dicyandiamidine  are  equally  indifferent. 
Xanthydrol  can  also  be  used  for  the  determination  of  urea  in 
the  blood.  To  rid  the  serum  of  albumin,  the  following  solution  is 
used : 
