24 MILK 
flask, 10 grams of powdered potassium sulfate 
and 15 to 25 c.c. (ordinarily about 20 c.c.) of the 
strong sulfuric acid are added and the diges- 
tion conducted as follows: The flask is placed 
in an inclined position and heated below the 
boiling-point of the acid for from five to fifteen 
minutes, or until frothing has ceased. Excessive 
frothing may be prevented by the addition of 
a small piece of paraffin. The heat is raised 
until the acid boils briskly. A small, short- 
stemmed funnel may be placed in the mouth 
of the flask to restrict the circulation of air. 
No further attention is required until the liquid 
has become clear and colorless, or not deeper 
than a pale straw. 
When Kjeldahl operations are carried out in 
limited number, the arrangement used in my 
laboratory has been found very satisfactory. A 
double-Y, terra cotta drain-pipe, about 20 cm. 
internal diameter, is connected by an elbow 
directly with the chimney-stack. The digestion 
flasks are supported as shown in the rough 
sketch, figure 1 (not drawn exactly to scale). 
Two flasks can be operated at once. The 
central opening is convenient for other opera- 
tions producing fumes. Openings not in use 
are closed by circles of heavy asbestos. 
Apparatus for use when many determinations 
are made are figured in the catalogs of supply- 
