22 
BULLETIN 1460, U. S. DEPARTMENT OF AGRICULTURE 
per cent in the moisture content of the samples submitted, enough 
difference to change appreciably the protein content of a sample of 
wheat, especially one of high protein content. 
DISTILLATION TECHNIQUE 
Investigations show that the outstanding factors necessary to 
obtain reliable results from the distillation side of protein testing 
are : Use of traps of sufficient size to prevent spray from being car- 
ried over during distillation ; more frequent " blank " determinations ; 
use of standard solutions of such strength that careful measurements 
will enable the analyst to work efficiently ; use of sufficient receiving 
acid to catch all the ammonia formed from samples having a large 
range in protein content ; use of sufficient reagent to precipitate the 
mercury when this is used as a catalyst ; and the accurate preparation 
of standard solutions. 
Table 15. — Moisture results obtained by various laboratories on two series of 
tvheat samples submitted m sealed tin containers 
Laboratory 
identification 
1 
2 
3 
4 
5 
16 
7 
8 
9 
10 
11 
2 12 
1-. 
P.ct. 
13.04 
12.75 
13.34 
P.ct. 
13. 28 
13.10 
13.77 
P.ct. 
11.51 
11.40 
11.86 
P.ct. 
12.33 
12.20 
12.75 
P.ct. 
12.27 
11.95 
12.56 
P.ct. 
10.49 
10.10 
10.58 
P.ct. 
11.04 
11.02 
P.ct. 
11.45 
11.41 
P.ct. 
13.35 
13. 17 
P.ct. 
10.23 
10.13 
P.ct. 
13.78 
13.57 
P.ct. 
12.70 
2 . 
12.54 
3 
4 
11.58 
11.74 
13.81 
10.58 
14.12 
13.07 
5. - 
13.64 
13.97 
12.14 
12.97 
12.78 
10.81 
6- - 
11.26 
9.94 
10.18 
10.95 
10.85 
11.58 
9.94 
1.64 
10.85 
10.40 
10.66 
11.15 
11.09 
11.74 
10.40 
1.34 
12.66 
12.40 
12.44 
13.50 
13.05 
13.81 
12.40 
1.41 
10.37 
9.42 
9.50 
10.50 
10.11 
10.58 
9.43 
1.15 
12.96 
12.98 
12.66 
13.82 
13.41 
14.12 
12.66 
1.46 
12.03 
7. 
12.37 
12.73 
11.10 
11.85 
11.45 
9.88 
12.01 
8 
11.80 
9 
Average 
Maximum 
Minimum 
Range 
13.05 
13.03 
13.64 
12. 37 
1.27 
13.20 
13.34 
13.97 
12.73 
1.24 
11.41 
11.57 
12.14 
11.10 
1.04 
12.26 
12.39 
12.97 
11.85 
1.12 
12.13 
12.19 
12.78 
11.45 
1.33 
10.29 
10.36 
10.81 
9.88 
.93 
12.65 
12.40 
13.07 
11.80 
1.27 
1 1 to 6, spring wheat. 
2 7 to 12, winter wheat. 
The experience of this laboratory has been an exact duplication of 
the findings of Paul and Berry. 13 On the subject of Kjeldahl traps, 
the necessity of using large double-lipped traps, whenever possi- 
ble, to obtain the best results, especially when the distillation is car- 
ried on rapidly, needs to be emphasized. The use of traps of various 
sizes and shapes on the same still will lead to erroneous results. 
Blank determinations should be run more frequently. Blanks are 
run by some of the collaborators only every week or every three or 
four clays. Blanks run on the same reagents for several successive 
days have been known to vary from 0.1 to 0.2 cubic centimeters of 
0.1N alkali. This in terms of protein is equal to 0.06 to 0.12 per cent. 
As for the strength of receiving acids, it is believed that the use of 
half normal solutions should be eliminated as their use introduces too 
great a chance for error. For convenience, especially when using a 
2-gram sample, 0.2 normal acid has given satisfaction. Solutions for 
back titrations should not be stronger than 0.1253 normal, preferably 
0.1 normal. 
As the usual wheat crop will have a protein content varying from 
8 to 20 per cent, it is necessary to have present sufficient acid to hold 
13 See footnote 8, 
