164 On the Jgency of the Carlonate nf Magnesia ' 



violent action, and fumes of acetic acid apparently mixed with a 

 little muriatic acid were disengaged. The excess of sulphuric 

 acid being expelled by heat, distilled water was added, and the 

 solution filtered. On treating it with carbonate of ammonia, 

 there was a copious light flocculent precipitate, which on further 

 examination proved to be carbonate of magnesia. A further 

 quantity of the original infusion of the bread was boiled down 

 to dryness in a platinum crucible ; it appeared to be principally 

 mucilage. On beini^ exposed to the atmosphere for a few hours, 

 it slightly deliquesced ; and when treated with strong sulphuric 

 acid ajid carbonate of ammonia, the results were similar to those 

 noticed above. 



On two ounces of fresh bread a half pint of distilled water 

 was poured. After remaining about twenty hours, the infusion 

 was decanted, and boiled down to about l-l'ith of its original 

 volume. It was put into a tubulated retort with a little strong 

 sulphuric acid, and a heat below the boiling point of the acid 

 was applied for half an hour. The neck of the retort was placed 

 in a glass containing a half cubic inch of pure water. A colour- 

 less fluid came over, which had a peculiar empyreumatic odour, 

 a very slight acid taste, and reddened litmus jiaper. This fluid 

 ^vas neutralized by caustic potash, and evaporated to dryness. 

 The dry mass was treated with a slight excess of strong sulphuric 

 acid; and on being gently heated very pungent fumes, principally 

 of acetic acid, were disengaged. An infusion of bread containing 

 no carbonate of magnesia, on being treated with carbonate of 

 ammonia gave no precipitate. A half pint of such an infusion 

 after being evaporated to drvness, and heated to redness for some 

 time, yielded a little white substance, which appeared to have 

 undergone fusion. It was soluble in water, gave no precipitate 

 witii the carbonates of potash and anunonia, but a copious one 

 with nitrate and nitrate of barvtes, and was merely the common 

 salt used in the bread. 



The foregoing experiments appear to sanction the conclusion, 

 that when the carbonate of magnesia is mixed in certain quan- 

 tities with the new flour, the magnesia acts chemically on the 

 bread in the act of baking. One portion of it is decomposed by 

 the acetic acid formed: the other part remains in its original 

 state. The disengagement of the carbonic acid gas from the 

 decomposed carbonate, may perhaps tend to increase the light- 

 ness and porosity of the bread. 



As the new flour appears to contain an excess of gluten, a very 

 tenacious substance, (on account of a portion of the farina of the 

 wheat having been converted into saccharine matter,) the unde- 

 compounded carbonate in the bread may exert a mechanical 

 agency on the gluten in the dough) and by lessening its cohesive 



property^ 



