TESTING WHEAT FOR PROTEIN 27 
GRINDING SAMPLE PREPARATORY TO CHEMICAL ANALYSIS 
Thirty to forty grams of wheat should be ground on a burr mill 
to such a degree of fineness that at least 60 per cent of it will pass 
through a No. 36 grits-gauze sieve. The burr mill should always 
be kept cool. The ground material should be immediately placed 
in a suitable air-tight container. The container should be of such 
size as to allow intimate mixing of the sample. 
The grinding apparatus should be thoroughly cleaned before each 
new sample of wheat is ground. This may be accomplished by dis- 
assembling the mill or by passing a sufficient quantity of the new 
sample through the burrs so that all traces of the previous sample 
will be entirely removed. 
CHEMICAL REAGENTS NECESSAY FOR MAKING PROTEIN TEST 
As a receiving acid for ordinary work, N/8 or N/10 acid is recom- 
mended. For standardizing hydrochloric and sulphuric acid the 
following methods are recommended. 
(a) Standard hydrochloric acid. — Determine the absolute strength 
as follows : Preliminary test : Place a measured portion of the acid 
to be standardized in an Erlenmeyer flask with excess of calcium 
carbonate to neutralize free acid and a few drops of potassium 
chromate as indicator by titration with silver nitrate solution deter- 
mine exactly the quantity required to precipitate the chlorides. 
Final determination : To a measured portion of the acid to be stand- 
ardized add from the burette 1 drop in excess of the required quan- 
tity of silver nitrate solution as determined by the preceeding test. 
Heat to boiling, protect from the light, and allow to stand until the 
precipitate is granular. Filter on a tared Gooch crucible, previously 
heated to 140-150° C, cool and weigh. 
(b) Standard hydrochloric acid {constant boiling point acid) 20 . — 
Make up HCL to a density of approximately 1.1, using a hydrometer. 
Distill off about three-fourths of this from an ordinary distillation 
flask, and discard the distillate. Continue the distillation of the 
remaining one-fourth, collecting this distillate in a separate con- 
tainer. This is the " constant boiling " acid, having a very definite 
composition which varies but slightly with variations in the atmos- 
pheric pressure at which the distillation is carried out. The desired 
quantity of this acid is. weighed out in an open dish on a sensitive 
balance. The open dish may be used since the acid is already in 
equilibrium with the air. 
The following tabulation shows the composition of constant boil- 
ing acid at various pressures, as well as the corresponding quantities 
necessary to give 1 gram-molecule of HCL. If this quantity is 
diluted to 1 liter, an exactlv normal solution of HCL results. If 
diluted to 10 liters exactly N/10 HCL results. 
20 Jour. Amer. Chem. Soc. vol. 31, p. 390. 
