15 



lated proteid cannot return to its orig-inal condition, thereby 

 differingf from a precipitated proteid. The temperature at 

 which coagulation occurs, depends upon the nature of the 

 proteid present, the reaction of the solution, and the presence 

 of neutral salts — e. g. an alkaline solution does not coagulate 

 on boiling, a neutral solution will do so partially, an acid so- 

 lution completely coagulates, provided the quantity of neutral 

 salts present is not too small. 



Albumins are soluble in water, coagulated bj heat, and 

 precipitated by saturating their solution with ammonium sul- 

 phate, and include ovalbumin (white of &gg), serum albumin 

 of blood serum and serous fluids, lactalbumin of milk, and 

 myo- albumin of muscle. 



In working through the experiments, a good general rule 

 to follow — unless otherwise directed— is not to use the whole 

 of the material or solution at once but only a small portion of 

 it ; so that other tests may be tried if necessary. 



2. Preparation of Egg- Albumin Solution. Break a small 

 hole in the end of a fresh tgg ; carefully pour out 10 cc. of the 

 white of the e.gg into a beaker. Let the yolk remain in the 

 shell and reserve for later use. Add about 200 cc. of distilled 

 water to the beaker containing the egg-white. Stir thoroughly 

 with a glass rod to break up the membranes and thus liberate 

 the albumin. Filter through a piece of muslin. Any opal- 

 escence is due to the precipitation of globulins. Egg-white 

 contains abdut 11%-12% of egg-albumin, together with small 

 quantities of globulins, grape-sugar, and mineral matter. The 

 white of one tgg will serve for a number of students. 



A good solution for laboratory use may also be prepared 

 by dissolving 1 gram of dry albumin in 200 cc. of distilled water. 



3. Heat 5 cc. of the albumin solution in a test-tube to 

 boiling. Notice the coagulation. Add a little nitric acid, the 

 coagulum may turn yellow but it does not dissolve. 



4. Xanthoproteic reaction. To a little of the albumin 

 solution in a test-tube, add some strong nitric acid ; a precipi- 

 tate is formed, white in color, which on being boiled, turns 

 yellow. After cooling, add ammonia till alkaline ; the yellow 

 color changes to orange. With weak solutions there may be 

 no precipitate at all. If only traces of albumin are present, 

 the yellow color with the nitric acid may fail to appear, but 



