[Vol. 2 



814 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



was also demonstrated in two other ways — by the formal- 

 doliyde-titration method of Sorenson ( '08), and the determina- 

 tion of the amino-nitrogen by the micro-Kjeldahl method of 

 Folin ('13). The Sorenson method consisted in adding 2 cc. 

 of formalin, made alkaline to a faint pink tinge with N/20 

 NaOH, to 10 cc. 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 cc. filtered portion of the 

 solution was precipitated with 2 cc. of a 25 per cent solution 



of phosphotungstic acid in 5 per cent H2SO4. The 

 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, 20X200 mm., 1 cc. concentrated H 2 S0 4 added, then 

 1 gram of K2SO4, and a drop of 5 per cent CuSO-t. 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 cc. 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 ; j being collected in a known volume of N/10 

 HC1. The acid in the collection ilask 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 NH3 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, 



