PROTEINS 235 



sodium hydrate. No coagulation occurs, as proteins do not coag- 

 ulate if heated in alkaline solution. 



ii. Concentrated Mineral Acids. Prepare three test tubes each 

 containing a few cubic centimeters of albumin solution. Add 

 concentrated sulphuric, hydrochloric, and nitric acid respectively 

 drop by drop to the three tubes, and record the results in each. 

 The albumin is precipitated in each tube. The coagulation with 

 nitric acid may be used to detect extremely small amounts of 

 protein. Dilute 1-2 c.c. of albumin solution with several volumes 

 of water. To a few cubic centimeters of this dilute solution in a 

 test tube, add concentrated nitric acid carefully from a pipette. 

 Caution. In taking up concentrated acids in a pipette, great 

 care should be exercised to avoid drawing the acid into the 

 mouth. Be sure the point of the pipette is kept well below the 

 surface of the acid, which should have been poured into a clean 

 test tube before being drawn up into the pipette. Do not fill 

 the pipette more than half full of acid. 



Run the nitric acid slowly into the albumin solution from the 

 pipette, keeping the point of the pipette at the bottom of the 

 test tube. This facilitates the formation of two layers. 



Observe the cloudy ring at the juncture of the two liquids. 

 Performed in this way, the test is known as the Heller Ring test, 

 and is used to detect the presence of protein in urine. 



iii. Alcohol. To a few cubic centimeters of albumin solution 

 add alcohol. The albumin is precipitated. 



iv. Heavy Metals. To small portions of albumin solution add 

 solutions of copper sulphate, mercuric chloride and lead acetate. 

 The albumin is precipitated by each reagent. Egg white is used 

 as an antidote in cases of poisoning by "blue vitriol,'' "corrosive 

 sublimate," etc., since it forms insoluble compounds with these 

 metal salts which then can be pumped from the patient's stomach 

 with a stomach pump, or removed by vomiting. The salts of most 

 heavy metals will precipitate proteins, in the same way as those 

 tested above. 



v. Acetic Acid and Potassium Ferrocyanide. To a few cubic 

 centimeters of albumin solution add 5-10 drops of 10% acetic 



