in improving Bread mads from the new Fiour. 163 



I was in consequence led to try the effects of the common car- 

 bonate of magnesia, a substance well known to be slightly al- 

 kaline. The trial was attended with perfect success; the im- 

 provement by the subcarbonate of magnesia was greater than by 

 any of the other alkaline bodies. 



The carbonate of magnesia, I conceived, might act on the 

 bread in two ways : chemically and meckanicuUy . Chemically, 

 by correcting its tendency to acidity ; — mechanically, by im- 

 proving its texture. I did not think it necessary to enter into 

 an elaborate analysis of the bread, in order to ascertain how far 

 jnv views were correct ; yet my experiments, some of which I 

 shall give in detail, have perhaps been sufficiently minute to 

 throw some light on the inquiry. 



Carbonate of magnesia, I found, improved the colour of bread 

 made from new seconds flour, whilst it impaired the colour of 

 bread from tine old and new flour. This circumstance favoured 

 the idea of its chemical action; for, if it were passive, it was in- 

 conceivable that a substance so jjerfectly white could in the 

 slightest degree injure the colour of the whitest flour. I made 

 the following experiments on bread from new seconds flour of 

 bad quality, containing the carbonate of magnesia in the quantity 

 of from 30 to 40 grains to a pound of flour. 



I burnt two ounces of the bread in a Hessian crucible, at a 

 low heat, until it became like a cinder ; the temperature was 

 then raised to a dull red ; and after twenty minutes the black 

 mass was partially covered with a light white substance, which, 

 on trial, readily dissolved in diluted sulphuric acid with eflcrve- 

 scence, and gave a white precipitate with carbonate of ammonia. 

 The heat was continued until all tlie carbonaceous matter had 

 disappeared, and there remained at the bottom of the crucible 

 a small quantity of a white earthy-like substance. It had a sa- 

 line taste, partially dissolved in water, and readily with efferve- 

 scence in sulphuric acid. It was principally common salt used 

 in the bread, and carbonate of magnesia. The preceding ex- 

 periments were repeated with similar results. 



I crumbled two ounces of the soft of the bread, and put it into 

 a pint of distilled water. After remaining about twenty-four 

 Jiours, the fluid was passed through a filter. (It was of a little 

 darker colour than the fluid furnished by bread made from new 

 or old fluur alone.) It had an agreeable taste, and did not affect 

 the colour of litmus. When the fluid was treated with a solution 

 of subcarbonate of annnonia, a light flocculent precipitate soon 

 made its appearance ; it was immediately redissolved with ef- 

 fervetccMce by a few drops of sulphuric acid. 



When a half |)int of the fluid was boiled down nearly to dry- 

 x\c<'%, and gently heated with strong sulphuric acid, there was a 



L 2 violent 



