366 



DETECTION OF SUBSTANCES. 



[CH. XIV. 



To a portion of the fluid, prepared as directed above, add an 

 equal bulk of saturated (NH 4 ) 2 SO 4 , shake vigorously, and filter 

 through a dryjpaper after about^ten minutes. 



Precipitate. 

 Scrape off the paper, 

 dissolve in a little hot 

 water, cool and add a 

 drop of iodine. A blue 

 colour shows the pres- 

 ence of starch. 



Filtrate. To a small portion add a drop or two 

 of iodine. If a reddish or purple colour be produced, 

 glycogen or dextrin is present. If the fluid be 

 opalescent after warming, glycogen is present. 

 Saturate the remainder with (NH<) 2 SO4 and filter. 



Precipitate. 

 Neglect. 



Filtrate. Add a drop of diluted 

 iodine, a red-brown colour shows 

 the presence of erythro-dextrin, 



(b) Apply Benedict's (Ex. TOO) or Fehling's test (Ex. 97) for 

 reducing sugars. Note that the tests do not succeed in the 

 presence of any considerable amount of ammonium salts. Also that 

 if albumoses, peptones or gelatin are present they should be 

 removed by alcoholic extraction as described in Ex. 58. 



(c) If a reduction be obtained, apply Barfoed's test (Ex. 101) 

 to distinguish between mono- and di-saccharides. The osazone test 

 (Ex. 109) also can be applied if necessary. 



(d) Test for cane-sugar and fructose (see Exs. 130 and 131). 



Table F. 



Examine the solution spectroscopically : gradually dilute the 

 solution, noting the spectrum at all stages of dilution. 



Take the reaction of the undiluted fluid to litmus paper, wash- 

 ing the surplus off the paper with a stream of distilled water, if you 

 are unable to note the reaction directly. 



If the fluid be neutral or alkaline, treat it with Stokes' fluid or 

 warm it with ammonium sulphide, and note whether the spectrum 

 is altered by reduction. This should be done after various dilutions 

 of the original solution. 



