106 PHYTOHORMONES 



coefficient between ether and water was found to be 9.4; 

 using this value and shaking into ether from solutions buf- 

 fered at different pH, the dissociation constant could be 

 determined. It was 1.8 X 10"^ or pK = 4.75, i.e. about 

 the same acid strength as acetic acid (for dissociation curve 

 see Figure 43, p. 131). The substance is destroyed by warm 

 acid but stable to warm alkali. Its extreme sensitivity to 

 oxidizing agents was taken to indicate presence of one or 

 more double bonds. Simultaneously and independently Kogl 

 and Haagen Smit (1931) made prehminary purifications of 

 the auxins formed by cultures of Rhizopus reflexus, yeast, 

 and b. coli. These products also behaved as acids. 



B. The Isolation of Auxins a and b 



At the same time Kogl and Haagen Smit (1931) found an 

 active substance to be present in large quantities in human 

 urine. The bicarbonate-soluble fraction of the ether extract 

 of urine was extracted with petroleum ether, and purified 

 by partition between benzene and aqueous alcohol; it was 

 then precipitated with lead acetate from weakly alkaline 

 70 per cent alcohol, treated with Ca(0H)2 to precipitate a 

 colored impurity, and finally heated with acid methanol. 

 This, instead of giving an ester, produced what turned out 

 to be a lactone. The product was distilled in vacuo (0.1 mm.), 

 when the bulk of the active substance distilled at 125°-130° C, 

 and yielded crystals of the acid C18H32O5 ("auxin a"). Both 

 acid and lactone were of about the same activity (approxi- 

 mately 50,000,000 AE per mg.). The method of purification 

 is summarized in Table VIII, which is taken from Kogl, 

 Haagen Smit, and Erxleben (1933). The extent of purification 

 from evaporated urine was about 20,000 to 50,000 times. 



Another active substance was subsequently isolated from 

 malt and from corn germ oil by a very similar purification 

 method (Kogl, Erxleben, and Haagen Smit, 1934). This 

 substance, C18H30O4, is isomeric with the lactone, but is an 

 acid and was named auxin b. It had the same activity as 

 auxin a. In a series of brilliant researches the constitutional 



