100 PUBLIC HEALTH CHEMISTRY 



formed. The porosity of bread, which is essential to its 

 easy digestion, is produced by enclosing in the dough 

 minute bubbles of carbonic acid gas. This is accomplished 

 in one of three ways, viz. : 



1. By the use of yeast which sets up fermentation of a 

 small portion of the starch, forming alcohol and carbonic 

 acid gas. 



2. By the use of baking-powders containing an acid salt 

 and a bicarbonate, which on being moistened give off 

 carbonic acid gas. 



3. By kneading the dough with water charged with 

 carbonic acid gas under pressure (Dauglish's system), 

 so-called " aerated bread." 



The " germ," an important constituent of the grain, and 

 rich in fat and proteid, is removed in modern milling 

 processes, and its absence makes the flour whiter. 



ANALYSIS. In sampling, take crumb and crust. 



Moisture. Take 10 to 50 grm. and dry to constant 

 weight in water-oven (should not exceed 40 per cent). 



Ash. Take 10 grm. of bread, moisten with strong 

 solution of ammonium nitrate, dry, and carefully ignite. 

 If ash is still very carbonaceous, repeat, and a clean ash 

 will usually be obtained (should not exceed 2 per cent, and 

 part insoluble in HC1 should not exceed 0-2 per cent). 



Alum. Take 10 grm. of bread free from crust, in a dish. 

 Pour over them 100 c.c. of water containing 5 c.c. each 

 of the logwood and ammonium carbonate solutions 

 described above. Stand for five minutes, drain off excess 

 of liquid, and dry in dish at iooC. Violet or blue tint if 

 alum is present ; if not, a brown or buff. Detects 7 grains 

 in a 4-lb. loaf. Test unreliable when bread is sour. 



Acidity. Soak 10 grm. of bread in 100 c.c. of aq. dest. 

 for one hour, macerate, and then titrate with N /io NaOH 

 and return result in terms of acetic acid : i c.c. N /io 

 NaOH = 0-006 grm. glacial acetic (part of the acidity is 

 due to lactic acid). Some extract with hot water, or digest 

 on water-bath and filter a portion. Use phenolphthalein 

 as indicator. Should be less than 0-115 P er cent or 8 gr. 

 per Ib. Alum test is unreliable when the bread is sour. 



Copper Sulphate has been detected in bread, probably 

 due to the corn having been steeped in a copper solution to 



