174 Dr. Colquhoun*s Essdy [Oct. 



It is not very efisy to penetrate the mode in which the treacle 

 thus acts upon the alkahne carbonate. By far the most probable 

 4jause seems to present itself in the probable existence of a 

 certain portion of uncombined acid in treacle, which, entering 

 into union with the alkali of the carbonate, releases a quantity 

 of carbonic acid gas. That such an acid does, in a greater or 

 less degree, always exist in treacle, seems proved by the fact, 

 that of many specimens which were examined in the course of 

 the experiments just mentioned, all possessed distinct traces of 

 acidity, and to an extent sufficient to enable them to communi- 

 cate a red colour to vegetable blues ; but the amount of uncom- 

 bined acid present in all these cases appeared to be very trifling, 

 and it was difficult to ascribe to its sole agency the production 

 of effects so striking. It cannot be doubted, however, that this 

 uncombined acid must operate to a certain extent in producing 

 a decomposition of the alkaline carbonate; and it may be 

 conjectured also, that the superiority in the expanding power of 

 old dough is occasioned either by the additional acidification of 

 a small quantity of the treacle, to which it would be disposed 

 during the keeping, by its state of mixture with the flour, or by 

 the circumstance that the carbonic acid gas disengaged by the 



had also a deep yellow colour, a sickening, and very unpleasant odour, and a nauseous 

 taste ; effects which were probably to be ascribed to some chemical action of tlic potashes 

 upon tlie flour. 



5. — Flour 4 ounces. 



Treacle.., ,. 3 ounces. 



Butter ^ ounce. 



Common crystallized car- 

 bonate 



^ Flour 4 ounces. 



Treacle 3 ounces. 



Butter ^ ^ ounce. 



Con)mori carb, of magnesia. 60 grains. 



The bread obtained in both of these trials possessed exactly the appearance -and 

 flavour of gingerbread prepared in tlie usual manner with potashes. And in these 

 cases also, the expansive property of the doughs was decidedly improved by keeping, so 

 that the results obtained by the substitution of cither of these alkaline carbonates in the 

 place of that more commonly used by the baker, werC, in all respects, perfectly parallel 

 to those which characterize his ordinary process. 



6. — Flour ....,..,,,,. 4 ounces. 



Treacle .;;;',;;;;;. 3 ounces. 



Butter ..;..;;.:;.. ^ ounce. 



Caustic potash 40 grains. 



Flour. 4 ounces. 



Treacle ./ .....^,.... S ounces. 



Butter. ..,..•.....*..'. .',■..■.. jounce. 



Calcined magnesia. 25 grains. 



The two doughs, compounded as above, were assayed both immediately after their 

 preparation, and at three successive intervals, a week being allowed to elapse between 

 each experiment. But in none of tlie trials was the bread possessed of the least vesicu- 

 larity : it was as compaqt aa if it had been prepared without the exhibition of any alkali 

 •whatever. 



:ffi'"r:?r:} •^^g'-- 



