BBEAD 503 



which, inasmuch as it is a bad conductor of heat, prevents the interior of the loaf 

 from being thoroughly baked, and at the same time opposes the free exit of the water 

 contained in the dough, and which the heat of the oven partly converts into steam ; 

 while the crust becomes thicker and darker than it otherwise should be, a sensible 

 loss of nutritive elements being sustained, at the same time, in the shape of pyrogenous 

 products, which are dissipated. 



The proportion of water retained in bread by undertaking is sometimes so large, 

 that a baker may thus obtain as much as 106 loaves from a sack of flour. 



The addition of boiled rice to the dough is also pretty frequently used to increase 

 the yield of loaves ; this substance, in fact, absorbs so much water that as many as 

 116 quartern loaves have thus been obtained from one sack of flour. 



Prom a groat number of experiments made with a view to determine the normal 

 quantity of water contained in the crumb of genuine bread, it is ascertained that it 

 amounts, in new bread, from 38 at least to at most 47 per cent. 



The quantity of water contained in bread is easily determined, by cutting a slice 

 of it, weighing 500 grains, for example, placing it in a small oven heated, by a gas- 

 burner or a lamp, to a temperature of about 220 F., until it no longer loses weight, 

 the difference between the first and last weighing (that is to say, the loss) indicating, 

 of course, the amount of water. 



Alum, however, is the principal adulterating substance used by bakers, almost 

 without exception, in this metropolis ; as was proved by Dr. Normanby in his evidence 

 before the Select Committee of the House of Commons, appointed in 1855, under 

 the presidenco of Mr. W. Scholefield, to inquire into the adulteration of food, drinks, 

 and drugs, which assertion was corroborated and established beyond doubt by the 

 other chemists who were examined also on the subject. 



The introduction of alum into bread not only enables the baker to give to bread 

 made of flour of inferior quality the whiteness of the best bread, but to force and 

 keep in it a larger quantity of water than could otherwise bo done. We shall see 

 presently that this fact has been denied, and on what grounds. 



The quantity of alum used varies exceedingly; but no appreciable effect is produced 

 when the proportion of alum introduced is less than 1 in 900 or 1,000, which is at the 

 rate of 27 or 28 grains in a quartern loaf. The use of alum, however, has become so 

 universal, and the Act of Parliament which regulates the matter has so long boon 

 considered as a dead letter, from the trouble, and chance of pecuniary loss which it 

 entails on the prosecutor should his accusation prove unsuccessful, that but few, and 

 until quite lately none, of the public officers would undertake the discharge of a duty 

 most disagreeable in itself and at the same time full of risk. 



When alum is used in making bread, one of the two following things may happen : 

 either the alum will be decomposed, as just said, in which case the alumina will, of 

 necessity, be set free as soon as digestion will have decomposed the organic matter 

 with which it was combined ; and thus it is presumable that either alum will be 

 re-formed in the stomach, or that, according to Liebig, the phosphoric acid of tho 

 phosphates of the bread, uniting with the alumina of the alum, will form an insoluble 

 phosphate of alumina, and the beneficial action of the phosphates will, consequently, 

 bo lost to the system ; and since phosphoric acid forms with alumina a compound 

 hardly decomposable by alkalis or acids, this may, perhaps, explain the indiges- 

 tibility of the London bakers' bread, which strikes all foreigners. letters on 

 Chemistry. 



The last defence set up in behalf of alumed bread to be noticed is, that, with 

 certain descriptions of flour, bread cannot be made without it ; that by means of 

 alum a large quantity of flour is made available for human food, which, without it, 

 must be withdrawn, and turned to some other less important uses, to the great 

 detriment of the population, and particularly of the poor, who would be the first 

 to suffer from the increase of the price of bread which such a withdrawal must fatally 

 produce. 



The process usually adopted for the detection of alum is that known as Kuhlmann's 

 process, which consists in incinerating about 3,000 grains of bread, porphyrising the 

 ashes so obtained, treating them by nitric acid, evaporating the mixture to dryness, 

 and diluting the residue with about 300 grains of water, with the help of a gentle 

 heat ; without filtering, a solution of caustic potash is then added, the whole is boiled 

 a little, filtered, the filtrate is tested with a solution of sal-ammoniac, and boiled for a 

 fow minutes. If a precipitate is formed it is not alumina, as hitherto thought and 

 stated by Kuhlmann and all other chemists, but phosphate of alumina, a circumstance 

 of great importance, not in testing for the presence of alumina, but for the determi- 

 nation of its amount, as will be shown further on, when entering into the details of 

 the modifications which it is necessary to make to Kuhlmann's process. 

 In a paper read in April 1858, at tho Society of Arts, Dr. Odling stated that out of 



