

[24*] 



SCHEME FOR TESTING A SOLUTION FOR THE MORE 

 COMMON PROTEIDS AND CARBO-HYDRATES. 



1. Note the reaction, and whether the liquid is coloured or colourless, clear or 

 opalescent. A reddish colour suggests blood ; opalescence suggests glycogen or 

 starch. Try one or more of the general proteid tests (e.g., the xantho-proteic or 

 biuret). If the result is positive, proceed as in 2 ; if negative, pass to 3. 



2. Test for Proteids. (i) If the reaction is acid or alkaline, neutralize with 

 very dilute sodium carbonate or sulphuric acid. A precipitate = acid- or 

 alkali-albumin, according as the original reaction is acid or alkaline. If the 

 original reaction is neutral, no acid- or alkali-albumin can be present in solution. 

 Filter off the precipitate, if any. 



(2) Boil some of the filtrate from (i) (or of the original solution if it is neutral), 

 acidulating slightly with dilute acetic acid. A precipitate = albumin or globulin. 

 Filter, and keep the filtrate. 



(3) If a precipitate has been obtained in (2), (a) saturate some of the original 

 solution with magnesium sulphate, or half saturate it with ammonium sulphate 

 (i.e., add to it an equal volume of saturated ammonium sulphate solution). If 

 there is no precipitate, globulin is absent, and therefore the precipitate obtained 

 in (2) must be albumin. A precipitate = globulin But albumin may also be 

 present in the solution. To see whether this is so, filter off the globulin and boil 

 the filtrate after acidulation with acetic acid. A precipitate = albumin. 



(b) Keep a small portion of the filtrate. Saturate the rest of the filtrate from 

 (2) with ammonium sulphate. A precipitate = proteose. Filter from (2) for (d). 



(c) To the filtrate from (b} add excess of solid sodium hydrate in small pieces 

 at a time. Much ammonia is given off. Allow the test-tube to stand fifteen 

 minutes, shaking it at intervals. Then add dilute cupric sulphate, and if much 

 of the sodium sulphate formed remains undissolved, add water to dissolve it. A 

 well-marked rose colour = peptone. 



(d) If proteoses have been indicated by (b), confirm by adding to the filtrate 

 from (2) strong nitric acid. A precipitate which disappears on heating and 

 reappears on cooling := proteose. But one of the members of the proteose group, 

 deutero-albumose, is not precipitated till sodium chloride is added as well as 

 nitric acid. This reaction will not detect small quantities of proteose. 



(4) If no precipitate has been obtained in (2), the solution contains neither 

 albumin nor globulin. To test whether proteose or peptone is present apply (3) 

 (6), (c), and (d}. 



3. Test for Carbo-hydrates. Use the original solution, freed from coagulable 

 proteids, if such have been found, by acidulation and boiling. 



(1) Add iodine. If the solution is alkaline neutralize it before adding the 

 iodine. A blue colour = starch. Confirm by boiling with dilute sulphuric acid 

 and testing for reducing sugar. A reddish-brown colour = glycogen or dextrin. 



Glycogen gives an opalescent, dextrin a clear, solution. Glycogen is precipi- 

 tated by basic lead acetate, dextrin is not. Both are changed into reducing sugar 

 by boiling with dilute acid. 



(2) Add to some of the original solution cupric sulphate and excess of sodium 

 hydrate, and boil. Yellow or red precipitate = reducing sugar. 



(3) If (i) and (2) are negative, boil some of the liquid with one-twentieth of its 

 volume of strong hydrochloric acid for fifteen minutes, and test as in (2). A red 

 or yellow precipitate shows that cane-sugar was originally present, and has been 

 inverted. 



