PROTEINS 273 



which should be borne in mind if the liquid to be tested has 

 been kept in a zinc lined can. 



12. Alkaloidal Reagents. Prepare six tubes of albumin solu- 

 tion and test the precipitating power of each of the following 

 reagents. Add a few drops of the reagent at a time, until a 

 precipitate forms, avoiding excess, as certain of the precipitates 

 are soluble in excess of the reagent : picric acid, tannic acid and 

 trichloracetic acid. Acidify the remaining three tubes with a few 

 drops of dilute hydrochloric acid before making the tests with: 

 phosphotungstic acid, phosphomolybdic acid and potassium mer- 

 curic iodide. An approximate estimation of the albumin in a 

 solution may be made by precipitating the protein in a specially 

 graduated tube, called an Esbach tube, by adding Esbach's re- 

 agent, which contains picric and citric acids. 



Ammonium or Magnesium Sulphate, Sodium Chloride, etc. 

 "Salting out." 



13. To about 3 c.c. of blood serum in a test tube add an equal 

 volume of water, and then powdered magnesium sulphate, (shak- 

 ing) until no more will dissolve. There should be considerable 

 excess salt in the tube to insure saturation. Globulins are thrown 

 down. Filter off the liquid. Test the precipitate for protein by 

 Millon's reaction. Test a portion of the filtrate by the xantho- 

 proteic test, not forgetting the addition of ammonia. If a pre- 

 cipitate forms, what is it ? To the remainder of the filtrate add 

 1-2 drops of dilute acetic acid. Explain. 



14. Repeat 13, using solid ammonium sulphate in the place 

 of magnesium sulphate. A copious precipitate should form. Fil- 

 ter and test filtrate and precipitate for protein as above. To a 

 portion of the filtrate add 1-2 drops of acetic acid. Explain. 



15. To a small portion of blood serum add an equal volume of 

 saturated ammonium sulphate solution, thus producing a mix- 

 ture half saturated with this salt ; this will have the same effect as 

 saturating with magnesium sulphate. 



16. Pour 2 or 3 drops of blood serum into a large beaker of 

 distilled water. The cloudiness is due to the precipitation of a 

 protein (globulin) which is soluble in the blood serum because of 



