57 



the two fluids. If the quantity of albumin is small, the 

 coagulum may not occur for a few minutes. 



Caution. A crystalline deposit of urea is sometimes ob- 

 tained with a very concentrated urine. If the urine contain 

 a large amount of urates, they may be deposited by the 

 acid, but the deposit in this case occurs above the line of 

 junction and di-sappears on heating. 



266. The ferrocyanide test. Into the bottom of a clean 

 test-tube is poured 15-30 drops of acetic acid, then 2-3 

 times that amount of 5% potassium ferrocyanide, and the 

 two ingredients thoroughly mixed by shaking the tube. 

 The urine is next added to the depth of two-thirds of the 

 test-tube. If albumin be present it will be thrown down 

 throughout the whole volume of the urine, in a more or less 

 milk like form, or flocculent cloud. 



As applied in this way it is said that this test acts upon 

 nothing but albumin. 



267. Picric acid test. (Johnson's.) Fill the test-tube half 

 full of urnie. Slightly incline the tube and gentlj' pour 

 down its .side about 2 cc. of a saturated aqueous solution of 

 picric acid, so that it may come in contact with the upper 

 layer of the urine. Place the tube in an upright position. 

 A layer of coagulated albumin will appear at the point of 

 junction. The coagulation of albumin takes place at once 

 and is thus not easily mistaken for precipitated urates, which 

 require some time for their precipitation and disappear on 

 the application of heat. 



268. Potassio-mercuric Iodide. (Tanret's Reagent.) This 

 solution is prepared according to the following formula : Po- 

 tas.sium iodide, 3.32 grams ; mercuric chloride, 1.35 grams ; 

 acetic acid, 20 cc; and enough distilled water to make 100 

 cc. The potassium iodide and mercuric chloride should be 

 dissolved separately, and the solutions mixed. Add a little 

 of this reagent to the suspected fluid and heat ; peptones, 

 urates, alkaloids and mucin are also precipitated at first but 



