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 only. 
proves the existence of sulphuric acid, it does not determine the na- 
ture of the sulphate. . ‘The following is the author’s method. 5 
Incinerate 200 grains of bread, porphyrise the cinders, treat it with 
nitric acid, evaporate to dryness, dilute with about 20 grains of distilled — 
water, add ee unfiltered mass pure caustic potash in excess, heat 
gently, filter, anid add muriate of ammonia, until the alumina is all 
precipitated, which is best effected by boiling a few minutes. Col- 
t the alumina on a filter, and determine by its weight the quantity 
of alum employed. 
It may be observed, sida that the incinerated bread of 
‘wheat or rye will give sometimes a precipitate of alumina without 
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 ;;';; of alum, gives an immediate precipi- 
tate of alumine, by this method. 
So small a quantity produces no effect upon the quality of the 
are and cannot be regarded as of any importance to health. 
al the weight of the ashes of burnt bread will furnish the means of a 
el good estimate ; 200 grains of = white bread give 1.27 to 
1.03 of ashes, while eed containing ;4; of alum, yield 1.6 of ashes. 
The latter is incinerated more easily, ies whiter ashes, and in much 
greater bulk. 
Sulphate of Zine 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 barytes, 
as in the case of alum. That of zinc as follows ;—digest 200 grs. 
ofthe 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 ammonia, filter, 
acidulate slightly by nitric acid; divide the fluid into two portions, 
Cd to one prussiate of potash, to the other hydro-sulphate of ammo- 
ma. Both of these reagents will shew the presence of zinc, by a 
white. precipitate, but: the first most decisively. The aes a: 
ought to be soluble in an excess of ammonia. 
