THE ALBUMINS. 287 



As nitric acid also precipitates certain resins which may have 

 been administered for medicinal purposes, it is at times necessary to 

 eliminate this possibility of error. Their presence is indicated if 

 the precipitate disappears on shaking the mixture with ether. 



The Boiling Test. The urine should present a feebly acid or 

 neutral reaction. If alkaline, it is rendered nearly neutral by adding 

 a drop or two of dilute acetic acid. A few cubic centimeters are 

 then boiled in a test-tube, when in the presence of coagulable 

 albumins the liquid becomes turbid, and on standing a flocculent 

 precipitate gathers at the bottom of the tube. The turbidity may, 

 however, at times be due to a precipitation of neutral earthy phos- 

 phates. To distinguish between the two, one or two drops of a 25 

 per cent, solution of nitric acid are now added for every 1 c.c. of 

 the urine. The earthy phosphates are thus dissolved, while the pre- 

 cipitate of albumin remains unaffected. If more than traces of 

 albumin are present, this test is very reliable ; otherwise there is 

 danger of dissolving the small amount of albumin. If nitric acid 

 is used instead of acetic acid, this danger is generally small, how- 

 ever, but the possibility exists, nevertheless. Hence in doubtful 

 cases it is always best to resort to the nitric acid test as well. 



If the albumin of Bence Jones should be present, coagulation 

 occurs at a temperature of 50 C. already, but it will be noted 

 that the precipitate disappears on subsequent boiling and reappears 

 on cooling. 



The common albumoses, as well as nucleo-albumin, are not 

 thrown down. The presence of the former may be inferred if 

 after the addition of the acid and subsequent cooling a white pre- 

 cipitate is formed, which dissolves upon the application of heat and 

 reappears on cooling. 



If acetic acid is to be employed instead of nitric acid, it is best 

 to treat the urine with one-sixth of its volume of a saturated solu- 

 tion of common salt, after having rendered it distinctly acid. It 

 is then boiled as before. In this case the danger of dissolving the 

 precipitated albumins is much lessened. 



The Potassium Ferrocyanide Test. A few cubic centimeters of 

 urine are strongly acidified with acetic acid, and treated with a 

 10 per cent, solution of potassium ferrocyanide drop by drop, when 

 in the presence of albumin a precipitation occurs which varies 

 in intensity with the amount present. Concentrated urines should 

 first be diluted. Albumoses are also thrown down, but are redis- 

 solved on boiling and reappear on cooling. Should nucleo-albu- 

 mins be present beyond traces, a precipitate develops upon the 

 addition of the acetic acid. This may also occur if urates are 

 present in large amounts. But in this event the precipitate clears 

 upon warming the solution ; and if the urine, moreover, is previously 

 diluted, it does not occur at all, while the separation of micleo-albu- 

 min takes place more rapidly in the latter case than before. 



Still other tests exist which are equally good, but for practical 



