BAKING POWDERS. 573 



digestive juices, and therefore does not produce the effect which is 

 attributed to the soluble forms of alum. Aluminium hydrate is insolu- 

 ble in water, but readily soluble in dilute acids, especially when freshly 

 precipitated. When heated it gradually loses its water of hydration, 

 but does not part with it entirely short of a very high heat. When 

 completely dehydrated it is insoluble even in dilute acid. It never 

 reaches this condition in baked bread, in which the temperature proba- 

 bly never, in the center of the loaf, at least, exceeds 100 0. 



Phosphate of aluminium is somewhat less soluble in dilute acids than 

 the hydrate. In the Norfolk case a'n effort was made by the prosecu- 

 tion to show that the soluble phosphates contained in the ash of flour 

 combined with the alum to form phosphate of aluminium, thus render- 

 ing them insoluble in the digestive juices, and depriving the flour of an 

 important constituent, and considerable evidence was offered by the 

 defense to show that this was not the case. Whether the addition to 

 alum powders of sufficient acid phosphate to combine with the aluminium 

 present as phosphate was the result of this discussion or not I can not 

 say, but it is certain that most of the alum powders now met with are 

 made in this way, so that if such a prosecution were to occur to day the 

 relative position of the parties would be reversed. It would be to the 

 interest of the alum-powder makers to show that phosphate of aluminium 

 is insoluble in the alimentary canal. The solubility of these compounds 

 in water or dilute acids is, of course, a question readily answered by any 

 chemist, but their solubility in the complex and various alimentary fluids, 

 and under the conditions of natural digestion in the human body, is quite 

 another matter. As might be expected, the testimony which has been 

 published upon this point is of the most conflicting character. Professor 

 Patrick, experimenting upon cats, found little or no solution of hydrate 

 of aluminium. Professor Pitkin, experimenting with gastric juice ob- 

 tained from a dog, found some solution, although he used phosphoric 

 acid in his powder. Professor Mallet, using an artificial gastric juice, 

 found some solution to occur, even with the phosphate, and considerably 

 more with the hydrate. It is not difficult to find reasons for such dis- 

 agreement in results, for. besides the various character of the solvents 

 used and the different conditions prevailing, it is easy to see that even if 

 the hydrate and phosphate of aluminium were themselves entirely in- 

 soluble, more or less aluminium would escape the reaction, either from 

 imperfect mixing of the powder in the dough or from improper propor- 

 tioning of the different ingredients in the powder itself, so that it would 

 go into the residue in the form of the original salt. With powders 

 specially prepared, on the other hand, and very carefully mixed, and 

 kneaded up thoroughly with the dough, it might be possible to find 

 but a very little dissolved in the digestive fluids under certain con- 

 ditions, even though the salts formed were slightly soluble in such 

 fluids. 



