178 Dr, Colquhoun'i Essay [Sept. 



dough became gradually sour. At the expiration of twenty-four 

 hours, upon opening up the dough, which was still in a state of 

 strong fermentation, a very acid odour was plainly perceptible. 

 The taste was also distinctly, though weakly acid. After taking 

 two pieces, weighing five ounces each, from the general mass, it 

 was once more set aside. Into one of the portions thus chosen 

 were kneaded 10 grains of the common carbonate of magnesia, 

 and then both were, after the usual manner, baked in the oven. 

 The difference between the two loaves, when baked, was most 

 striking. The bread which had been made from the sour dough 

 alone had a taste distinctly perceptible of acidity, and a smell so 

 sour as must have rendered it almost unsaleable, while that 

 which contained the magnesia presented not the slightest indi- 

 cations of any kind of sourness, and appeared in all respects an 

 excellent loaf. 



This was certainly a very decisive proof of the advantage with 

 which this carbonate may be employed in correcting an acidity, 

 which had proceeded to as great a degree as it is ever met with 

 by the baker in his ordinary practice. But it appeared desirable 

 both in a practical and in a theoretical view, to try the effect of 

 the same substance on a still greater degree of acidity, and also 

 to compare its relative action with that of carbonate of soda on 

 the same acid. Accordingly that mass of sour dough from 

 which two portions had been taken, as above-mentioned, was 

 allowed to remain for twenty-four hours longer in a warm situa- 

 tion as before. At the end of this period, the various processes 

 of internal decomposition had not wholly ceased, and it was 

 found to be still in a state of fermentation, though not so vigo- 

 rous as on the preceding day. The acid taste of the dough had 

 by this time very much increased, and the acid odour was strong. 

 Four portions of this dough were now taken, all of which were 

 baked after the usual form ; but with this difference in their 

 composition, that one was put into the oven made of the sour 

 dough just as it stood, a second had four grains, and a third 

 eight grains of the carbonate of magnesia kneaded up with them, 

 and to the fourth were added 16 grains of the common crystal- 

 lized carbonate of soda. The first loaf, when baked, possessed, 

 in a very rank and strong degree, both a taste and a smell of 

 acidity. In the second, the acidity remained faintly perceptible, 

 especially in the smell. In the third, the loaf had no acid or 

 other disagreeable peculiarity whatever. In the fourth, there 

 was no acid taste, but a slightly acid smell. 



These results appear quite decisive. For thus the exhibition 

 of eight grains of the carbonate of magnesia to five ounces of 

 dough, or about 32 grains to the pound, which is about 52 grs. 

 to the pound of flour, proved amply sufficient to correct an 

 acidity which had been allowed to proceed to an extreme hardly 

 ever known in practice. And indeed in the great bulk of 



