Use of Sulphate of Copper, <^c. in Bread. 273 



alum, but he does not deem it sufficiently exact to prove the exist- 

 ence of very small portions of alum, for he obtains a precipitate in that 

 way, from bread without alum. The water with which the flower is 

 mixed generally contains sulphate of lime, and as the barytic test pnly 

 proves the existence of sulphuric acid, it does not determine the na- 

 ture of the sulphate. The following is the author's method. 



Incinerate 200 grains of bread, porphyrise the cinders, treat it with 

 nitric acid, evaporate to dryness, dilute with about 20 grains of distilled 

 watery add to the unaltered mass pure caustic potash in excess, heat 

 gently, filter, and add rnuriate of ammonia, until the alumina is all 

 precipitated, which is best effected by boiling a few minutes. Col- 

 lect the alumina on a filter, and determine by its weight the quantity 

 of alum employed. 



It' may be observed, however, that the incinerated bread of 

 wheat or rye will give sometimes a precipitate of alumina widiout 

 any addition of alum, but in quantity so small, that its weight would 

 occasion no sensible error in estimating the amount of the salt. It 

 may be derived from earthy particles adherent to the grain, or from 

 the hearth of the oven in which the bread is baked. 



Bread which contains 3 ^V o o^' aliun, gives an immediate precipi- 

 tate ofalumine, by this method. 



So small a quantity produces no effect upon the quality of the 

 bread, and cannot be regarded as of any importance to health. 



The weight of the ashes of burnt bread will furnish the means of a 

 pretty good estimate ; 200 grains of pure white bread give 1.27 to 

 1.03 of ashes, while bread containing ^^^ of alum, yield 1 .6 of ashes. 

 The latter is incinerated more easily, gives whiter ashes, and in much 

 greater bulk. 



Sulphate of Zinc has been, it appears, occasionally used in bread. 

 As incineration might volatilize the zinc, the analysis must be man- 

 aged in the humid way. 



The presence of the acid may be detected by muriate of baryles, 

 as in the case of alum. That of zinc as follows ; — digest 200 grs. 

 of the crumb in cold distilled water, press the fluid through a linen 

 cloth, filter through paper, evaporate by gentle heat, till the liquid be- 

 comes somewhat viscid ; add to it an excess of liquid auniionia, filter, 

 acidulate slightly by nitric acid ; divide the fluid into two portions, 

 add to one prussiate of potash, to the other hydro-sulphate of ammo- 

 nia. Both of these reagents will shew the presence of zinc, by a 

 white precipitate, but the first most decisively. The precipitate 

 ought to be soluble in an excess of ammonia. 



