PRACTICAL EXERCISES 21 



down, which is turned reddish on boiling. If only traces of proteid 

 are present, no precipitate is caused, but the liquid takes on a red tinge. 



(5) Heat a portion to 30 C. on a water-bath. Saturate with 

 crystals of ammonium sulphate; the albumin is precipitated. Filter, 

 and test the filtrate for proteids by (3). None, or only slight traces, 

 will be found. The sodium hydrate must be added in more than 

 sufficient quantity to decompose all the ammonium sulphate. It 

 will be best to add a piece of the solid hydrate. Peptones are not 

 precipitated by ammonium sulphate, but all other proteids are. 



2. Special Reactions of Groups of Proteids (i) Coagulable Pro- 

 teids : (a) Native Albumins. (a) Heat a little of the solution of 

 egg-albumin in a test-tube ; it coagulates. With another sample 

 determine the temperature of coagulation, first slightly acidulating 

 with dilute acetic acid a drop or two of a 2 per cent, solution. 



71? determine the Temperature of Coagulation. Support a beaker 

 by a ring which just grips it at the rim. Nearly fill the beaker with 

 water, and slide the ring on the stand till the lower part of the beaker 

 is immersed in a small water-bath (a tin can will do quite well). In 

 this beaker place a test-tube, and in the test tube a thermometer, 

 both supported by rings or clamps attached to the same stand. Put 

 into the test-tube at least enough of the albumin solution to com- 

 pletely cover the bulb of the thermometer, and heat the bath, stirring 

 the water in the beaker occasionally with a feather, or a splinter of 

 wood, or a glass rod, the end of which is guarded with a piece of 

 indiarubber tubing. Note the temperature at which the solution 

 becomes turbid, and then the temperature at which a distinct coagu- 

 lum or precipitate is formed. 



(P) A similar experiment may be performed with serum- albumin. 

 obtained as on p. 60. 



(b) Globulins. Use serum- globulin (p. 60), or myosinogen (p. 626). 

 Fibrinogen is also a globulin, but cannot easily be obtained in 

 quantity. Verify the following properties of globulins : 



(a) They coagulate on heating. 



(P) They are insoluble in distilled water (p. 60). 



(y) They are precipitated by saturation with magnesium sulphate 

 or sodium chloride (p. 60). 



They give the general proteid tests (i) to (5). 



(2) Derived Albumins or Albuminates (a) Acid-albumin. To 

 a solution of egg-albumin add a little "2 per cent, hydrochloric acid, 

 and heat to about body temperature say 40 C. for a few minutes. 

 Acid-albumin is formed. It can be produced from all albumins and 

 globulins by the action of dilute acid. Make the following tests : 



(a) Add to a portion of the solution in a test-tube a few drops of 

 a solution of litmus ; the colour becomes red. Now add drop by 

 drop sodium carbonate or dilute sodium hydrate solution till the 

 tint just begins to change to blue. A precipitate of acid-albumin is 



in its own weight of strong nitric acid, and add to the solution thus 

 obtained twice its volume of water. Let it stand for a short tiro*, and 

 then decant the clear liquid, which is the reagent. 



