PROTEIDS. 3 



2. Presence of Nitrogen and Sulphur in Albumin. 



(a.) Place some powdered dried albumin in a reduction 

 tube, and into the mouth of the tube insert (1) a piece of red 

 litmus paper, and (2) a lead acetate paper. On heating the 

 tube the former becomes blue from the escape of ammonia, 

 which can also be smelt, and the latter black from the for- 

 mation of lead sulphide. 



(b.) Heat some dry proteid with excess of soda-lime in a 

 hard dry tube, when vapour of ammonia is evolved. 



(c.) Place a few grains of the dry proteid, with a small 

 piece of metallic sodium, in a dry hard tube, and heat 

 slowly at first, and then strongly. After cooling, add care- 

 fully 3 cc. of water to the NaOy residue, filter, and to the 

 filtrate add a few drops of ferric chloride and ferrous sul- 

 phate, and then add excess of hydrochloric acid. If nitrogen 

 be present, there is a precipitate of Berlin blue, sometimes 

 only seen after standing for a time. 



3. Determination of Temperature of Coagulation. "A glass 

 beaker containing water is placed within a second larger beaker 

 also containing water, the two being separated by a ring of cork. 

 Into the water contained in the inner beaker there is immersed 

 a test-tube, in which is fixed an accurately graduated thermo- 

 meter, provided with a long narrow bulb. The solution of the 

 proteid, of which the temperature of coagulation is to be deter- 

 mined, is placed in the test-tube, the quantity being just sufficient 

 to cover the thermometer bulb. The whole apparatus is then 

 gradually heated, and the experimenter notes the temperature at 

 which the liquid first shows signs of opalescence " (Gamgee). 



4. Circumstances Modifying the Coagulating Temperature. 

 Place 5 cc. of the solution of albumin in each of three test-tubes, 

 colour them with litmus, and label them A, B, C. To A add a 

 drop of very dilute acetic acid (Ol per cent, acetic acid diluted 

 five or six times) ; to B add a very dilute solution of caustic soda 

 (0-1 per cent, of soda or potash similarly diluted) ; C is neutral 

 for comparison. Place all three tubes in a beaker with water 

 and heat them gradually, noting that coagulation occurs first in 

 A, next in 0, and last of all in B, the alkaline solution. 



