[VoL. 2 
814 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
was also demonstrated in two other ways—by the formal- 
dehyde-titration method of Sorenson (’08), and the determina- 
tion of the amino-nitrogen by the micro-Kjeldahl method of 
Folin (713). The Soérenson method consisted in adding 2 ce. 
of formalin, made alkaline to a faint pink tinge with N/20 
NaOH, to 10 ce. of the filtered protein solution, made alkaline 
to the same color. Upon mixing, the color disappeared and 
the acidity resulting was titrated against N/50 NaOH, using 
phenylphthalein as an indicator. 
In the determination of the amino-nitrogen by the ‘‘micro’’ 
method of Folin, the protein in a 5 ee. filtered portion of the 
solution was precipitated with 2 ec. of a 25 per cent solution 
of phosphotungstic acid in 5 per cent H2SO4. The precipitate 
was filtered off and a 2 cc. portion of the filtrate removed for 
the determination of the nitrogen. Duplicate determinations 
were made in all cases. These portions were placed in Jena 
test-tubes, 20200 mm., 1 ee. concentrated H2SO4 added, then 
1 gram of K2SOx4, and a drop of 5 per cent CuSO4. The 
digestion was carried on over the flame from a micro burner, 
the fumes being carried away by the fume adsorbers described 
by Folin. Usually 20 minutes sufficed for the completion of 
the digestion, although in a few instances 25 minutes were 
required. After cooling slightly, 6 ec. of distilled water were 
carefully added. The tubes were then transferred to the 
distilling apparatus where concentrated NaOH was added to 
alkalinity, and the tube contents distilled over for three 
minutes, the NH; being collected in a known volume of N/10 
HCl. The acid in the collection flask was titrated against N/10 
NaOH with alizarin red (alizarin sulfonsaure Natrium, 
Merck), and the amount of nitrogen represented by the 
acid neutralized, determined. 
In the method originally described by Folin, the NHs3 was 
not distilled but was forced over from an alkaline solution by 
a strong air current. However, students in his laboratory 
have made use of a micro distilling apparatus, and the sug- 
gestion for the ones employed here owes its origin to one of 
Folin’s assistants. Distillation has the advantage of quick- 
ness, and from the writer’s experience, of accuracy as well, 
