[Vor. 3 
408 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
3. Micro-burners; 
4. Ostwald pipettes of 1 and 2 cc. capacity; 
9. Condensers of small size.! 
The fume absorption apparatus consists of two parts: (1) 
a piece of straight glass tubing with side arms, (2) the fume 
absorber proper. This latter is a 25-сс. pipette, one end of 
which is invaginated into the bulb, the other bent midway at 
a little more than right angles. The invaginated end sits into 
the neck of the digestion flask, while the other end fits into a 
side arm of the glass tubing. The latter, in turn, connects 
to the suction pump, by which the fumes are drawn off. Both 
the Kjeldahl flasks and the tubing are supported in the man- 
ner illustrated in pl. 7. 
In the Folin modification, Jena test-tubes (200x:25 mm.) 
are used in digestion. In this laboratory the small Kjeldahl 
flask has been found to be better adapted to plant material, 
beenuse of the relatively high percentage of carbohydrates 
present, and the tendency of these to froth. 
The material, if in solution, is added to the digestion flask 
by means of a calibrated Ostwald pipette; if in solid form, as 
plant organs or sections, it is carefully dried and weighed. 
The quantity of material taken for digestion must be deter- 
mined by a preliminary rough analysis, since the method is 
best adapted for amounts of nitrogen between .5 and 5 mg. 
One сс. (more if needed) of chemically pure sulphuric acid 
(сопс.) is added to the material to be digested, the amount 
depending upon the quantity of carbon-containing compounds 
present, then 1 gram of potassium sulphate and a drop of 
5 per cent copper sulphate. The contents are heated slowly 
until frothing is over, after which a hotter flame may be 
employed. Sometimes it is necessary to add some solid frag- 
ment to prevent bumping, a bit of unglazed porcelain being 
especially good. Small mica chimneys can be obtained to 
protect the flames from air currents, but lacking these bot- 
tomless beakers may be used. 
Upon completion of digestion the contents of the flask are 
permitted to cool somewhat (the liquid must not become 
1 The condensers can be made in the laboratory from glass tubing. 
