268 Dr, Colquhoun's Essay [Oct. 



tliose proportions in which they pretty exactly saturated each 

 other. Tne mode iu which these experiments were conducted, 

 was by first intimately blending the flour with the alkaline car- 

 bonate, in the state of a fine powder, and next making this 

 mixture into dou^h with the requisite quantity of a water holding 

 the acid in solution. And especial care was taken during the 

 kneading to confine as large a quantity of gas as possible within 

 the dough, in order to give the system a fair trial. The mixtures 

 employed in these experiments were, respectively, in the four 

 proportions following : 



1 . — 4 ounces flour. 



42 grains sesqui-carbonate of soda. 

 90 grains dilute muriatic acid. 



By previous experiment, this quantity of dilute acid had been 

 ascertained to be requisite to saturate exactly 42 grains of ses- 

 qui-carbonate of soda. 



2. — 4 ounces flour. 



20 grains sesqui-carbonate of soda. 

 19 grains tartaric acid. 



3. — 4 ounces flour. 



30 grains carbonate of magnesia. 

 15 grains tartaric acid. 



4. — 4 ounces flour. 



60 grains carbonate of magnesia. 

 30 grains tai'taric acid. 



These several masses of dough, after being duly kneaded, 

 were set aside for about 20 minutes, so as to afford full space 

 for a sufficient reaction to ensue between the acid and the car- 

 bonate : they were then baked, in the usual manner, in an oven. 



During the process of kneading the specimens of dough into 

 loaves, they had all of them felt loose, light, and spongy, to an 

 uncommon degree, and they were also vesicular and bulky when 

 first introduced into the oven. These characters plainly indi- 

 cated the sudden generation of a great volume of elastic fluid 

 within the dough. Yet in every instance the bread formed 

 from them proved doughy and sad, possessed but a few diminu- 

 tive vesicles, and was never piled. Of all the varieties, that in 

 which the flour had been mixed with sesqui-carbonate of soda 

 and tartaric acid approached the nearest to a good loaf, and 

 might have been termed hght or porous when compared with 

 bread made of unfermented dough. But even this specimen in 

 point of true hghtness and elastic vesicularity was decidedly 

 inferior to our common loaf-bread. 



Jndeed it seems plain, from reflecting on the use and necessity 



