io INTRODUCTION 



solution of litmus; the colour becomes red. Now add drop by drop 

 sodium carbonate or dilute sodium hydroxide solution till the tint just 

 begins to change to blue. A precipitate of acid -albumin is thrown 

 down . Add a little more of the alkali, and the precipitate is redissolved . 

 It can be again brought down by neutralizing with acid. 



08) Heat a portion of the solution to boiling; no precipitate is formed. 

 (y) Add strong nitric acid ; a precipitate appears, which dissolves on 

 heating, and the liquid becomes yellow. 



(b) Alkali-albumin. To a solution of egg-albumin add a little sodium 

 hydroxide, and heat gently for a few minutes. Alkali-albumin is 

 produced. It can be derived by similar treatment from any albumin 

 or globulin. 



(a) Neutralize, after colouring with litmus solution, by the addition 

 of dilute hydrochloric or acetic acid. Alkali-albumin is precipitated 

 when neutralization has been reached. It is redissolved in excess of 

 the acid. 



(/3) To another portion of the solution of alkali-albumin add a few 

 drops of sodium phosphate solution, then litmus, and then dilute acid 

 till the alkali-albumin is precipitated. More of the dilute acid should 

 now be required to precipitate the alkali-albumin, since the sodium 

 phosphate must first be changed into acid sodium phosphate. 



(y) On heating the solution of alkali-albumin there is no coagulation. 

 (2) Proteoses. For preparation and reactions, see p. 452. They 

 differ from albumins and globulins in not being coagulated by heat, and 

 from meta-proteins in not being precipitated by neutralization. They 

 are soluble (with the exception of hetero-albumose) in distilled water, 

 and are not precipitated by saturation of their solutions with mag- 

 nesium sulphate or sodium chloride. Saturation with ammonium sul- 

 phate precipitates them. With a solution of ' commercial peptone,' 

 which consists chiefly of albumoses, and contains only a little true 

 peptone, perform the following tests: 



(a) Boil the slightly acidulated solution; there is no coagulation. 

 ()3) Biuret reaction, p. 8. 



(y) To a portion of the solution add its own volume of saturated 

 ammonium sulphate solution. The primary albumoses (proto- and 

 hetero-albumose) are precipitated. Filter. Add a drop of sulphuric 

 acid to the filtrate and saturate it with ammonium sulphate crystals. 

 The secondary or deutero-albumoses are precipitated. Filter. The 

 filtrate still contains peptones. Use it for (3). 



(3) Peptones. For preparation and tests, see p. 453. They differ 

 from heat-coagulable proteins and meta-proteins in the same way as 

 proteoses, and they differ from proteoses in not being precipitated by 

 ammonium sulphate. On the filtrate from (2) perform the biuret test, 

 as described in (7), p. 8; and note that the pink colour is the same as 

 that given by proteoses. 



Carbo-Hydrates. 



i. Glucose or Dextrose. Make a solution of dextrose in water, and 

 apply to it Trommer's test for reducing sugar. Put some of the dextrose 

 solution in a test-tube, then a few drops of cupric sulphate, and then 

 excess of sodium or potassium hydroxide. The blue precipitate of 

 cupric hydroxide which is first thrown down is immediately dissolved 

 in the presence of dextrose and many other organic substances. Now 

 boil the blue liquid, and ac^ellow or red precipitate (cuprous hydroxide 

 or oxide) is formed. 



