Am  jour.  Pharm.  j        zinc  and  Copper  in  Gelatin.  a87 
Tune,  1919.      J  rt  ^<J/ 
No. 
Hydrolysis  Method. 
Digestion  Method. 
Cu  P. p.m. 
Zn  P. p.m. 
Cu  P. p.m. 
Zn  P.p.m. 
I34I-0 
I34I-0 
I34I-0 
I34O.O 
I  
I34I-0 
2  
126.0 
122.0 
128.0 
3  
32.0 
96.4 
32.O 
96.4 
3-'  
26.6 
104  0 
32.0 
96.4 
4  
20.0 
64.O 
20.0 
68.0 
4  
24.O 
56.O 
20.0 
56.0 
5  
24.O 
77-9 
24.O 
80.3 
Ip.  • 
22.4 
80.3 
24.O 
80.3 
5  
20.0 
803 
76.0 
The  copper  was  separated  but  was  not  determined  in  samples  1 
and  2  because  at  first  it  was  intended  only  to  investigate  the  deter- 
mination of  zinc. 
In  order  to  test  the  method  further,  measured  quantities  of 
standard  solutions  of  zinc  and  copper  were  added  to  weighed 
amounts  of  sample  5.  The  hydrolysis  and  analyses  were  made  as 
described  above  with  the  following  results : 
Sample  Taken, 
Grams. 
Cu  Added,  Mg. 
Zu  Added,  Mg. 
Cu  Found,  Mg. 
Zu  Found,  Mg. 
20 
2-5 
2.8 
2-5 
2.7 
20 
3-0 
3-1 
3-1 
3-2 
20 
2-5 
4-7 
2.4 
4-7 
20 
2.0 
3-1 
1.9 
3-2 
It  should  be  observed  that  the  amount  of  zinc  and  copper  in  20 
Gm.  of  sample  5  gelatin  as  determined  by  averaging  the  results  ob- 
tained by  previous  analysis,  has  been  deducted  from  the  results 
given  above.  The  results  obtained  with  these  analyses  show  that 
the  method  is  accurate. 
In  order  to  obtain  satisfactory  results,  it  is  most  important  that 
the  directions  be  followed  in  every  detail.  Furthermore,  great  care 
must  be  taken  to  eliminate  by  filtration  any  non-volatile  matter 
which  may  separate  during  the  course  of  the  analyses,  before  pro- 
ceeding to  make  the  final  precipitation  of  the  zinc  or  copper  sul- 
phides. Also,  the  Gooch  crucibles  used  must  be  prepared  so  that 
they  will  not  lose  weight  during  the  filtration  and  ignition  of  the 
sulphides. 
Bureau  of  Chemistry, 
Department  of  Agriculture, 
Washington,  D.  C. 
