236 PHYSIOLOGICAL CHEMISTRY 



acid and then, drop by drop, potassium ferrocyanide. A pre- 

 cipitate forms. Avoid an excess of the reagent, as the precipitate 

 may be redissolved. This test is very delicate. Zinc also will give 

 a similar precipitate with ferrocyanide, a fact which should be 

 borne in mind if the liquid to be tested has been kept in a zinc 

 lined can. 



vi. 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. 



vii. Ammonium or Magnesium Sulphate, Sodium Chloride, etc. 

 "Salting out." 



(a) 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. A positive 

 test should result, since the filtrate still contains serum albumin, 

 which is not precipitated under the above conditions. To the 

 remainder of the filtrate add 1-2 drops of dilute acetic acid. A 

 precipitate results, as albumins are precipitated by saturating 

 with magnesium sulphate in acid solution. 



(b) Repeat (a) 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. The 

 precipitate should give a positive protein test. The filtrate 



