BAKING POWDERS. 



575 



(fc) Partial precipitation in insoluble form of some of the organic matter of food 

 may probably also be brought about by the presence of the aluminium compounds in 

 question. 



(I) From the general nature of the results obtained, the conclusion may fairly be 

 deduced that, not only alum itself, but the residues which its use in baking-powder 

 leaves in bread, can not be viewed as harmless, but must be ranked as objectionable, 

 and should be avoided when the object aimed at is the production of wholesome 

 bread. 



COMPARISON OF THE DIFFERENT CLASSES OF POWDERS IN RE- 

 SPECT TO THEIR RELATIVE AERATING STRENGTH AND THE 

 AMOUNT OF RESIDUE LEFT BY EACH. 



The following comparison of the different powders described may 

 prove interesting. It is assumed, of course, that the ingredients are 

 combined in exactly the proper proportions, and that all the chemicals 

 used are of full purity and strength: 



From this it will be seen that a tartrate powder, theoretically, gives 

 the lowest percentage of carbonic-acid gas in proportion to the weight 

 of chemicals used in its composition, together with the least weight of 

 residue ; and a straight alum powder gives the highest proportion of 

 gas, with the greatest weight of residue. It is assumed that burnt alum 

 is used in both the alum and the alum and phosphate powders. The 

 residues are calculated to hydrated salts in all cases. No account is 

 made of inert "filling," as that would be the same in each case. It 

 should of course be remembered that in the above calculation the total 

 weight of residue is reckoned in each case without regard to solubility 

 or relative effect upon the system of the various salts formed. This has 

 been sufficiently discussed under the different classes. 



CARBONATE OF AMMONIA. 



This salt is used to some extent as an ingredient in baking-powders. 

 It is also often used alone by bakers as a chemical aerating agent. It 

 does not necessarily require an acid to set free its gases, being vola- 

 tilized without decomposition simply in heating. The commercial salt, 

 familiar to everybody as " smelling-salts," or sal volatile, is obtained by 

 subliming a mixture of two parts of chalk and one part of sal ammoniac 



