Chemistry. 351 



(Phil. Mag. for March.) He is of opinion that the process of nitrifica- 

 tion is promoted by the water containing carbonic acid, by the aid of 

 which carbonate of lime is dissolved, and thus presented in a state more 

 favourable to chemical action. He supposes putrefying organic remains to 

 be of use by yielding an abundant supply of carbonic acid. 



17. Alcohol derived from the Fermentation of Bread.-— In the last 

 Number of this Journal we gave an extract from Dr Colquhoun's Es- 

 say on the art of baking bread, and in confirmation of the views there 

 stated, we insert the following letter addressed by Mr Thomas Gra- 

 ham to the editors of the Annals of Philosophy. " Two facts of consider- 

 able importance in determining the nature of the pannary fermentation 

 have been made known by your very ingenious correspondent on the art 

 of baking bread. He has shown that the fermentation depends upon the 

 saccharine ingredient of the flour, by renewing it when exhausted by the 

 addition of sugar; and provided for the little alteration in the proportion 

 of sugar existing in the flour, before and after fermentation, by exhibiting 

 the influence of the baking in converting a portion of starch into sugar. 

 From the known laws of the decomposition of sugar, it is presumed, with 

 considerable reason, that the fermentation is the vinous. The production 

 of alcohol in the course of the fermentation of bread in baking, which we 

 have found to take place, and rendered appreciable, is perhaps a most irre- 

 fragable proof of which this theory is susceptible. 



" To avoid the use of yeast, which might introduce alcohol, a small quan- 

 tity of flour was kneaded, and allowed to ferment in the usual way, to 

 serve as leaven. By means of the leaven, a considerable quantity of flour 

 was fermented ; and when the fermentation had arrived at the proper 

 point, formed into a loaf. The loaf was carefully inclosed in a distillatory 

 apparatus, and subjected for a considerable time to the baking tempera- 

 ture. Upon examining the condensed liquid, the taste and smell of alco- 

 hol were quite perceptible, and by repeatedly rectifying it, a small quanti- 

 ty of alcohol was obtained of strength sufficient to burn, and to ignite gun- 

 powder by its combustion. 



" The experiment was frequently repeated, and in different bakings the 

 amount of alcohol obtained, of the above strength, found to vary from 0.3 

 to 1 per cent, by weight of the flour employed. When the fermented 

 flour was allowed to sour before baking, the amount of alcohol rapidly di- 

 minished ; and in all cases, the disagreeable empyreuma completely dis- 

 guised the peculiar smell of the alcohol, when in its first diluted state, and 

 in vapour." 



18. On the confinement of Dry Gases over Mercury. — The results of an 

 experiment made by Mr Faraday, and quoted as such, having been deem- 

 ed of sufficient interest to be doubted, he has been induced to repeat it 

 and though the original experiment was not published by him, he is in- 

 clined to put the latter and more careful one upon record, because of the 

 strong illustration it affords of the difficulty of confining dry gases over mer- 

 cury alone. Two volumes of hydrogen gas were mixed with one volume 



