ADVANCED CHEMICAL PHYSIOLOGY 333 



ated to dryness on a waterbath in a weighed crucible. The crucible 

 is carefully heated over a free flame until a perfectly dry and black ash 

 has been obtained. The flame is now strengthened and the ash is 

 heated until it becomes white. The crucible is then allowed to cool in a 

 desiccator, after which it is weighed. 



Flour. 



I. Determine moisture and ash by ordinary methods. 



II. Determine total nitrogen by Kjeldahl method. Use about 1 gm. 

 of flour. T.N. X 5-7 gives gluten content. 



III. Determine nature of proteins present. 



Make about 30 gms. of flour into a stiff dough with 1215 c.c. water 

 and allow the mass to stand for an hour. It is then carefully kneaded, 

 in a stream of water, over a sheet of fine muslin, which allows the starch 

 to pass through, but retains any particles of gluten, or the mass may be 

 wrapped in linen and then kneaded. The ball of gluten thus obtained 

 is tough and elastic and can be pulled out into threads. After washing 

 the ball of gluten is left for an hour under water, and then the excess 

 of moisture removed by squeezing. Gluten consists of two proteins : 

 gliadin, which is soluble in dilute alcohol, and glutenin which is soluble 

 in very dilute alkali. If the mass of crude gluten obtained as above be 

 extracted with 70 per cent, (by volume) alcohol gliadin goes into solution 

 and can be precipitated by the addition of sodium chloride. The 

 amount present in gluten may be estimated by carrying on the alcohol 

 extraction for two hours and determining the amount of nitrogen in the 

 filtrate. The nitrogen value multiplied by 5-7 gives the gliadin content. 



IV. Determination of carbohydrate. 



3 gms. of the flour are extracted with 50 c.c. of cold water for an 

 hour with frequent stirring. The mixture is filtered (if there is any 

 difficulty the addition of 2 c.c. of alumina cream helps) and the reiidue 

 washed with water until filtrate equals 250 c.c. The soluble carbo- 

 hydrate can be estimated in the filtrate both before and after hydrolysis. 

 The insoluble residue is transferred to a flask, fitted with a reflux 

 condenser, 200 c.c. of water and 20 c.c. strong HC1 (sp. gr. 1-125) are 

 added. Heating is continued for two and a half hours and then the 

 contents are cooled, nearly neutralised with strong NaOH, made up to 

 250 c.c., filtered, and the dextrose determined in an aliquot portion of 

 the filtrate. The gravimetric Fehling method (see p. 304) serves 

 excellently. Dextrose value multiplied by 0-9 gives weight of 

 starch. 



Egg. -The nature of the proteins present and their coagulation 

 temperature can be determined in " white of egg." 



The presence of lipoids can be determined in egg-yolk which contains 

 fat, lecithin, cholesterol and a phospho-protein vitellin. 



Extract the yolk with ether by repeated shaking in a flask. 

 Cautiously evaporate, by placing the porcelain basin containing the 

 ethereal extract on a previously heated waterbath (use no flame] 

 or preferably on an electric hot-plate, to small volume. Add acetone 

 until a distinct precipitate is formed crude lecithin. Filter off the 

 precipitate. Keep the filtrate which contains cholesterol (and some 

 lecithin). 



Precipitate. Dissolve the precipitate by means of alcohol and drop 

 slowly, with stirring, the alcoholic solution into water. A white 

 precipitate results " lecithin." Saponify some of this emulsion by 

 heating with caustic alkali. (Note odour of trimethylamine. ) Addition 



