520 THE POPULAR SCIENCE MONTHLY. 



ing packets of " stuff " or " rocky," or any other bleaching abomina- 

 tion. 



Liebig asserts that in certain cases the use of lime-water improves 

 the quality of bread. Tomlinson says that, " in the time of bad har- 

 vests, when the wheat is damaged, the flour may be considerably im- 

 proved, without any injurious result whatever, by the addition of from 

 twenty to forty grains of carbonate of magnesia to every pound of 

 flour." It is also stated that chalk has been used for the same pur- 

 pose. These would all act in nearly the same manner by neutralizing 

 any acid that might already exist or be generated in the course of 

 fermentation. 



When gluten is kept in a moist state it slowly loses its soft, elastic, 

 and insoluble condition ; if kept in water for a few days, it gradually 

 runs down into a turbid, slimy solution, which does not form dough 

 when mixed with starch. The gluten of imperfectly ripened wheat, 

 or of flour or wheat that has been badly kept in the midst of humid 

 surroundings, appears to have fallen partially into this condition, the 

 gluten being an actively hygroscopic substance. 



Liebig's experiments show that flour in which the gluten has under- 

 gone this partial change may have its original qualities restored by 

 mixing one hundred parts of flour with twenty-six or twenty-seven 

 parts of saturated lime-water and a sufficiency of ordinary water to 

 work it into dough. I suspect that the action of the alum is of a 

 similar kind, though this does not satisfactorily account for the bleach- 

 ing. 



The action of sulphate of copper, which has been used in Belgium 

 and other places for improving the appearance and sponginess of 

 loaves, is still more mysterious than that of alum. Kuhlmann found 

 that a single grain in a four-pound loaf produced a marked alteration 

 in the appearance of the bread. Fortunately, this adulteration, if per- 

 petrated to a mischievous extent, may be easily detected by acidulat- 

 ing the crumb, and then moistening with a solution of ferrocyanide 

 of potassium. The brown color thus produced betrays the presence 

 of copper. The detection of alum is difficult. 



I should add that the ancient method of effecting the fermentation 

 of bread, and which I understand is still employed to some extent in 

 France, differs somewhat from the ordinary modern practice described 

 in my last. When flour made into dough is kept for some time mod- 

 erately warm, it undergoes spontaneous fermentation, formerly de- 

 scribed as " panary fermentation," and supposed to be of a different 

 nature from the fermentation which produces yeast. 



Dough in this condition is called leaven, and when kneaded with 

 fresh flour and water its fermentation is communicated to the whole 

 lump ; hence the ancient metaphors. In practice the leaven was ob- 

 tained by setting aside some of the dough of a previous batch, and 

 adding this when its fermentation reached its maximum activity. One 



