10 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



(a) The characteristic odour of burning flesh, horn, hair, feathers, &c., has 

 been already noted, and, though only a rough test, is very trustworthy. 



(b) Take a little dried albumin and mix it thoroughly in a mortar with 

 about twenty times the amount of soda-lime and heat in a test-tube over a 

 Bunsen flame. Ammonia comes off in the vapours produced, and may be 

 recognised by (i.) its odour ; (ii.) it turns moistened red litmus paper (held over 

 the mouth of the tube) blue ; (iii.) it gives off white fumes with a glass rod 

 (held over the mouth of the tube) which has been dipped in hydrochloric acid. 



(c) Mix some dried albumin with about ten times its weight of a mixture 

 of equal parts of magnesium powder and anhydrous sodium carbonate. A 

 small quantity of the mixture such as would lie on the end of a penknife 

 is then carefully heated in a dry test-tube and finally heated more strongly 

 for about half a minute to red heat. Dip the tube while still glowing into 

 a beaker containing a few c.c. of distilled water ; the tube will break and its 

 contents mix with the water. Filter and label the nitrate A ; add to this 

 nitrate a little strong solution of potash, one or two drops of cold saturated 

 solution of ferrous sulphate and a drop of ferric chloride solution. Bring 

 the mixture to boiling point, then cool and acidify with hydrochloric acid. 

 The fluid becomes bluish green, and gradually a precipitate of Prussian blue 

 separates out. This test is due to the fact that some of the nitrogen is 

 fixed as sodium cyanide, and this gives the Prussian blue reaction with the 

 reagents added. 



7. Tests for Sulphur. (a) In the foregoing test (6 c) the sulphur of the 

 albumin combines with the sodium to form sodium sulphide. This may be 

 detected by taking some of the nitrate A and adding freshly prepared solution 

 of sodium nitro-prusside ; a reddish violet colour forms. 



(b) Test for loosely combined Sulphur. Add two drops of a neutral 

 lead acetate solution to a few c.c. of caustic soda solution. The precipitate 

 of lead hydroxide which is first formed soon dissolves. Heat a small portion 

 of the albumin with this alkaline solution. The mixture turns black in con- 

 sequence of the formation of lead sulphide, part of the sulphur present in 

 albumin in the unoxidised form having been split off from it by the caustic 

 soda as sodium sulphide. 



(c) Take some dried albumin and fuse with a mixture of potash and 

 potassium nitrate. Cool ; dissolve in water and filter. The filtrate will give 

 the following tests for sulphates : Acidulate with hydrochloric acid and add 

 barium chloride ; a white precipitate of barium sulphate is produced. 



(d) Take some solution of albumin and heat in an open dish in a fume 

 cupboard for at least an hour with large excess of fuming nitric acid, renewing 

 the acid from time to time as necessary. The resulting fluid will give the 

 test for sulphate as in c. 



8. Test for Phosphorus. The two tests just described (7 c and d) may be 

 repeated with some substance (such as caseinogen, nucleoprotein, or lecithin) 

 which contains phosphorus in organic combination ; or the organic matter 

 may be more conveniently destroyed by Neumann's method, which consists 

 in heating it with a mixture of sulphuric and nitric acids. The resulting 

 fluid in each case gives the following test for phosphates : Mix it with half 

 its volume of nitric acid ; add ammonium molybdate in excess and boil ; a 

 yellow crystalline precipitate falls. 



The reactions described in the foregoing exercises show how the 

 processes of pure chemistry may be employed for the detection of 

 some of the most important elements that occur in substances of 

 physiological importance, and thus form a fitting introduction to a 

 study of physiological chemistry. 



