Practical physiological chemistry : a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . reproduced in Fig. 85, p. 239. Re-crystallize a little urea from water in thesame way and compare the crystals withthose obtained from the alcoholic solution. 5. Formation of Biuret.—Place a small amount of urea ina dry test-tube and heat carefully in a low flame. The ureamelts at 1320 C. and liberates ammonia. Continue heatinguntil the fused mass begins to solidify. Cool the tube, dis-solve the residue in dilute potassium hydroxide solution andadd
Practical physiological chemistry : a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . reproduced in Fig. 85, p. 239. Re-crystallize a little urea from water in thesame way and compare the crystals withthose obtained from the alcoholic solution. 5. Formation of Biuret.—Place a small amount of urea ina dry test-tube and heat carefully in a low flame. The ureamelts at 1320 C. and liberates ammonia. Continue heatinguntil the fused mass begins to solidify. Cool the tube, dis-solve the residue in dilute potassium hydroxide solution andadd very dilute cupric sulphate solution (see p. 45). The Melting-point TubesFastened to ofThermometer. 244 PHYSIOLOGICAL CHEMISTRY. purplish-violet color is due to the presence of biuret which hasbeen formed from the urea through the application of heat asindicated. This is the reaction: NH22 C = 0 NH2 Urea. NH2 C = 0 \ NH + NHa /C = 0 NH2 Biuret. 6. Urea Nitrate.—Prepare a concentrated solution of ureaby dissolving a little of the substance in a few drops of a drop of this solution on a microscopic slide, add a drop Urea Oxalate. of concentrated nitric acid and examine under the microscope. Compare the crystals with those reproduced in Fig. 86, p. 242. 7. Urea Oxalate.—To a drop of a concentrated solution of urea,prepared as described in the last experiment(6),add a drop URINE. 245 of a saturated solution of oxalic acid. Examine under themicroscope and compare the crystals with those shown in page 244. 8. Decomposition by Sodium-Hypobromite.—Into amixture of 3 of concentrated sodium hydroxide solutionand 2 of bromine water in a test-tube introduce a crystalof urea or a small amount of a concentrated solution of the influence of the sodium-hypobromite, XaOBr,the urea is decomposed and carbon dioxide and nitrogen areliberated. The carbon dioxide is absorbed by the excess ofsodium hydroxide while the nitrogen is evolved
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