GENERAL QUALITATIVE TESTS FOR PROTEIDS 1 63 



6. If a coagulable proteid is present its temperature of coagula- 

 tion should be determined in the following manner : Some of the 

 solution is placed in a test-tube in which is inserted a thermometer. 

 Suspend the test-tube in a beaker of water, and set this beaker 

 in a second containing an amount of water sufficient to reach the 

 level of the first and heat very gradually over a Bunsen flame. 

 The temperature at which turbidity is at first noticeable and also 

 the point at which the precipitation becomes flocculent should be 

 carefully noted. The globulins vary greatly in their coagulation 

 temperatures, but usually do not fall below 55° C. After the 

 first flocculent precipitate is obtained by this method remove it by^ 

 filtering and return the filtrate to the water-bath. Raise the tem- 

 perature as before and note any further changes. It is possible 

 to make several such fractional coagulations at successively higher 

 temperatures in solutions in which several proteid substances are 

 present. 



7. Treat a portion of the solution of the precipitate from the 

 dialyzer, with solid magnesium sulphate in excess, which will 

 precipitate globulins. 



If the above treatment indicates that the substance is a proteid 

 it should be washed thoroughly, first with alcohol, and then with 

 ether and dried in a thermostat to a constant weight at 1 io° C, 

 or at room temperature over sulphuric acid. 



Other substances are often thrown down with the globulins 

 upon dialysis, and an effort should be made to obtain the proteid 

 as pure as possible. This may be done in various ways. Dis- 

 solving the proteid in a saline solution as dilute as may serve, fil- 

 tering and repeatedly dialyzing may accomplish the desired result. 

 Dissolving the proteid in the smallest amount of saline solution 

 that would serve, filtering and adding to the filtrate a larger vol- 

 ume of distilled water, will often precipitate the globulins in pure 

 form. 



It is usually necessary to determine the percentage of the ele- 

 ments, especially the nitrogen contained in order to identify any 

 globulin. The total proteid of a tissue can be approximately es- 



