396 PHYSIOLOGICAL CHEMISTRY. 



is easily prevented in the heat test with acetic acid, by acidifying 

 another portion with acetic acid at the ordinary temperature. Mucin 

 and nucleoalbumin substances similar to mucin are hereby precipi- 

 tated. If in the performance of the heat and nitric acid test a 

 precipitate first appears on cooling or is strikingly increased, then 

 this shows the presence of albumoses in the urine, either alone or 

 mixed with coagulable albumin. In this case a further investiga- 

 tion is necessary (see below). In a urine rich in urates a precipi- 

 tate consisting of uric acid separates on cooling. This precipitate 

 is colored, sandy, and hardly to be mistaken for an albumose or 

 albumin precipitate. 



HELLER'S test is performed as follows (see page 19): The urine 

 is very carefully floated on the surface of nitric acid in a test-glass. 

 The presence of albumin is shown by a white ring between the 

 two liquids. With this test a red or reddish-violet ring is always 

 obtained with normal urine; it depends on the indigo coloring mat- 

 ters and can hardly be mistaken for the white or whitish albumin 

 ring, and this last must not be mistaken for the ring produced by 

 bile-pigments. In a urine rich in urates another complication may 

 occur, due to the formation of a ring produced by the precipitated 

 nric acid. The uric-acid ring does not lie, like the albumin ring, 

 between the two liquids, but somewhat higher. For this reason we 

 may often have two simultaneous rings with urines rich in urates 

 and yet not containing very much albumin. The disturbance 

 caused by uric acid is easily prevented by diluting the urine 

 with 1-2 vol. water before performing the test. The uric acid now 

 remains in solution, and the delicacy of HELLER'S test is so great 

 that after dilution only in the presence of insignificant traces of 

 albumin does this test give negative results. In a urine very rich 

 in urea a ring-like separation of urea nitrate may also appear. This 

 ring consists of shining crystals, and it does not appear in the pre- 

 viously-diluted urine. A confusfon with resinous acids, which also 

 give a whitish ring with this test, is easily prevented, since these 

 acids are soluble on the addition of alcohol. A liquid which con- 

 tains pure mucin does not give a precipitate with this test, but it 

 gives a more or less strongly opalescent ring, which disappears on 

 stirring. The liquid does not contain any precipitate after stirring, 

 but is clear or somewhat opalescent. If we bear in mind the 

 above-mentioned possible mistakes and the means by which they 

 may be prevented, there is hardly another test for albumin in the 

 urine which is at the same time so easily performed, so delicate, and 

 so positive as HELLER'S. With this test even 0.02 p. m. albumin 

 may be detected without difficulty. In performing this test the 

 (primary) albumoses are also precipitated. 



The reaction with metaphosphoric acid (see page 19) is very 

 convenient and easily performed. It is not quite so delicate and 



