TESTIXG WHEAT FOE PROTEIN" 29 
(A) Granulated zinc or pumice stone. 
(i) Sodium sulphide or sodium thio sulphate. — Use 50 cubic centi- 
meters of a solution containing 40 grams of sodium sulphide per liter 
or 50 cubic centimeters of a solution containing 80 grams of sodium 
thiosulphate per liter. 
(j) Powdered potassium or sodium sulphate free from nitrogen-: 
A mixture of G parts of K 2 S0 4 and 4 parts of Na 2 S0 4 will prevent 
the formation of the acid cake which forms when Xa 2 SO is used 
separately. 
(k) Sodium hydroxide solution. — A saturated solution should be 
prepared having a specific gravity between 1.43 and 1.48. It is ad- 
vantageous to dissolve the mercury precipitant in the alkali and add 
both to the digestion flask at the one operation. 
(/) Methyl-red solution. — Dissolve 1 gram of methyl red in 100 
cubic centimeters of 95 per cent alcohol. 
APPARATUS 
For distillation any suitable flask of about 550 to 800 cubic centi- 
meters capacity may be used. It is fitted with a rubber stopper 
through which passes the lower end of a Kjeldahl connecting bulb to 
prevent sodium hydroxide from being carried over mechanically 
during distillation. The bulb should be about 5 centimeters in diam- 
eter and the outlet tube should be of the same diameter as the con- 
denser tube with which the upper end of the bulb is connected. A 
double-lipped connecting bulb is preferable. 
The most essential feature of the digestion and distillation appa- 
ratus is the condition of the heating units, for heat is the outstanding 
factor in the matter of obtaining rapid protein tests. 
Providing gas is used as a source of heat, to obtain the most rapid 
results, the burners on the digestion apparatus should be adjusted 
so that heat enough is developed to boil away 150 cubic centimeters 
of water from 200 cubic centimeters in 20 minutes when the 200 cubic 
centimeters volume is placed in a Kjeldahl flask of 550 cubic centi- 
meters capacity. At this intensity of heat digestion will be complete 
inside of one hour. 
With the usual type of electric heater the period of digestion for 
those delivering 450 watts should be one hour. The period of diges- 
tion should be 45 to 50 minutes with a heater delivering 550 watts, 
and for those heaters delivering over 600 watts a 40 to 45 minute 
digestion should be used. Great care should be exercised with heat- 
ers of the last-mentioned capacity as acid evaporation at this inten- 
sity is very rapid and disastrous results are often obtained with this 
type of heater. 
The gas heaters on the distillation apparatus should be adjusted to 
develop enough heat to distill over 150 cubic centimeters of water in 
25 to 30 minutes. 
DETERMINATION 
Place 1 gram of the sample in a digestion flask together with 
approximately 7 to 10 grams of a mixture containing by weight 6 
grams of potassium sulphate, 4 grams of sodium sulphate, and one- 
half gram of red mercuric oxide. Acid 20 to 25 cubic centimeters of 
sulphuric acid, thoroughly mix the acid, salts, and sample together 
