190 THE PROTEIN SUBSTANCES. 



HN CO 



I I 

 Uracil, C 4 H 4 N2O2, = OC CH (2, 6-dioxypyrimidine), was first 



HN CH 



obtained by As COLI and KOSSEL from yeast nucleic acid and later obtained 

 from various complex nucleic acids, perhaps secondarily from the cytosine 

 as a cleavage product. The synthetical preparation was first accomplished 

 by E. FISCHER and RoEDER. 1 



Uracil crystallizes in needles which cluster in rosettes. On careful 

 heating it sublimes in part undecomposed, but develops red vapors and 

 decomposes in part. It is readily soluble in hot water, but less so in cold 

 water, and nearly insoluble in alcohol and in ether. Uracil is readily 

 soluble in ammonia. It is precipitated by mercuric nitrate, but not by 

 phosphotungstic acid. It is precipitated by silver nitrate only on the 

 careful addition of ammonia or baryta-water. Uracil gives the WEIDEL 

 reaction and the following reaction described by WHEELER and JOHNSON : 2 

 The uracil solution is treated with bromine-water until it is permanently 

 cloudy and then treated with baryta-water, when a purple or violet-col- 

 ored precipitate appears almost immediately. The coloration varies 

 with the dilution. This reaction which, as remarked above, is also given 

 by cytosine, depends upon the fact that dibromoxyhydrouracil is first 

 formed, and from this, by the action of the barium hydroxide, first isodi- 

 aluric and then dialuric acid is produced, both of which give the colora- 

 tion. In regard to the preparation of uracil see KOSSEL and STEUDEL. S 



HN CO 



Thymine, C 6 H fl N 2 2 , = OC C.CH 3 (5-methyluracil) . This body, 



HN CH 



which is identical with nucleosin obtained by SCHMIEDEBERG from sal- 

 mo-nucleic acid, was first prepared by KOSSEL and NEUMANN from thymus- 

 nucleic acid, and then by other investigators, especially LEVENE and 

 MANDEL, from other animal nucleic acids. FISCHER and ROEDER and 

 recently GERNGROSS 4 have prepared it synthetically. 



Thymine crystallizes in small leaves grouped in stellar or dendriform 



1 Ascoli, Zeischr. f. physiol. Chem., 31; Kossel and Steudel, ibid., 37; Levene, 

 ibid., 38, 39; Levene and Maiidel, ibid., 49; E. Fischer and Roeder, Ber. d. d. chem. 

 Gesellsch., 34. 



2 Journ. of biol. Chem., 3. 



3 Zeitschr. f. physiol. Chem., 37. 



4 Schmiedeberg, Arch. f. exp. Path. u. Pharm., 37; Kossel and Neumann, Ber. 

 d. d. chem. Gesellsch., 26 and 27; Mandel and Levene, Zeitschr. f. physiol. Chem., 46, 

 47, 49, 50; E. Fischer and Roeder, ibid., 34; Gerngrose, ibid., 38. 



