Am*octufi8^7.arm'}        Volumetric  Estimation  of  Urea.  495 
equation) ;  and  if  56  gm.  of  CaO  equal  or  represent  60  gm.  of  CO 
(NH2)2,  then  0*14003  gm.  of  CaO  (the  amount  contained  in  the  110 
ce.  of  lime-water  employed)  equals  0.15  gm.  of  urea,  thus  : 
56    :'  60    :  :    0*J4003    :  0*15. 
Then  if  you  employ  110  cc.  of  lime-water  and  if,  after  the  opera- 
tion, you  subtract  from  the  number  0'15,  the  quantity  of  urea  corre- 
sponding to  the  lime  not  precipitated  by  C02  in  the  110  cc.  of  lime- 
water,  you  will  have  the  quantity  of  urea  corresponding  to  the  lime 
precipitated.  In  order  to  know  the  quantity  of  urea  corresponding  to 
the  CaO  not  precipitated  (which  remains  in  solution),  take  from  the 
product,  that  one  molecule  of  oxalic  acid  neutralizes,  one  molecule 
of  CaO,  and  this  corresponds  analytically,  to  one  molecule  of  urea. 
Then,  if  1000  cc.  of  the  above  oxalic  acid  solution  corresponds  to  1*5 
gm.  of  urea,  1  cc.  corresponds  to  0  0015  gm.  of  urea.  Therefore  mul- 
tiply the  number  of  the  cc.  of  the  solution  of  oxalic  acid  used  (to 
neutralize  the  10  cc.)  by  0*0015,  which  equals,  equivalently,  the 
quantity  of  urea  in  1  cc,  or,  which  is  the  same  thing,  multiply  that 
number  by  0*0165  for  11  times  the  proportion)  this  will  give  the 
urea  corresponding  to  the  lime  left  in  solution),  and  subtract  this 
quantity  of  urea  from  0*15  (urea  corresponding  to  the  lime  contained 
in  110  cc.  of  lime-water);  the  difference  represents  the  urea  corre- 
sponding to  the  lime  precipitated  and  contained  in  the  liquid  analyzed. 
Dr.  Campari  gives  the  results  of  a  number  of  determinations,  first, 
upon  a  solution  of  urea,  25  to  1000,  and  then  upon  urine,  in  com- 
parison with  the  well-known  process  of  Liebig ;  the  latter  results  are 
as  follows  : 
Urine  used.  Oxalic  Acid  used         Urea  in  1  Liter,         Urea  in  1  Liter, 
forlOcc.'of  Lime- Water.  (Campari.)  (Liebig.) 
2  cc.  6*6  cc.  20*55  gm.  20*20  gm. 
2  cc.  6*3  cc.  23*05  gm.  22*90  gm. 
2  cc.  6*45  cc.  21*80  gm.  21*55  gm. 
2  cc.  6*95  cc.  17*70  gm.  17*35  gm. 
These  results,  according  to  the  author,  demonstrate  that  this  nitrous 
acid  method  conduces  to  the  best  results  obtainable.  But  in  order  to 
secure  absolutely  accurate  results,  it  is  necessary  that  the  heating  of 
the  flask  be  slow,  in  order  to  avoid,  especially,  the  raising  of  the 
vapor  of  nitric  acid  that  could  be  formed,  by  the  decomposition  with 
the  sulphuric  acid,  from  the  potassium  nitrate,  always  present  in  the 
commercial  nitrite. 
