CHEMICAL SCIENCE. 339 



4 



this way for the detection of adulteration with alum, die results must be 

 quite fallacious. Many experiments have been made in this way, namely, 

 by the macerating process, and some persons \vao have done so have given 

 testimony that they have found alum in the bread ; but it must be clear that 

 they were satisfied with simply testing the watery liquid from the bread by 

 the chloride of barium and the ammonia, and concluded that the precipitates 

 they obtained were from the sluphtiric acid and alumina of the alum. Bv 



tf * i. 



experiment it was ascertained that a much larger amount of alum might 

 have been added to the bread than was done in this case, and the same con- 

 clusions arrived at. 



These results prove that the alum is decomposed in the baking of the 

 bread ; the alumina of the alum combining with the phosphoric acid, of the 

 phosphates already in the flour, forms phosphate of alumina, a salt perfectly 

 insoluble in water. 



Objection was made to the other process, which was to incinerate the 

 bread and dissolve the ash in dilute nitric acid, and test for the alumina in 

 the solution, on account of the very long time before the organic part of the 

 bread is burnt away ; and it was proposed to simply char the bread, and 

 afterwards to deflagrate the coaly mass with nitre, and then to add water 

 only; the carbonate of potash formed by the deflagration of the nitre, dis- 

 solves up, and along with it nearly all the alumina, alumina being very con- 

 siderably soluble in a carbonate of potash solution, and from which chloride 

 of ammonium in excess will precipitate it. 



Another process for detecting when alum has been used in the baking of 

 bread, founded upon the mordanting properties of the sales of alumina, was 

 given, and it was said to be accurate, and if so it is easy; it is simply to im- 

 merse for a few hours a piece of the suspected bread in a fresh and dilute 

 decoction of logwood, made with ordinary pump water ; pure bread is said to 

 be superficially stained by the pale orange-red color of the decoction, whilst 

 alumed bread is dyed a purple color, and to some depth. 



It was stated it was difficult to judge of the quantity of the alumina 

 simply by the eye, since its appearance varies much with the mode of its 

 precipitation. 



OX THE CHEMICAL PROPERTIES OF THE POTATO. 



At the last meeting of the British Association Mr. J. TV. Rogers pre- 

 sented a paper " on the chemical properties of the potato, and its uses as a 

 general article of commerce if properly manipulated," the object of which 

 was to show that the matter of the potato was in reality equal in nutrit re- 

 value to the dry matter of wheat, whilst the quantum of food produced from 

 a given quantity of land was nearly four times that produced from wheat. 

 He exhibited some interesting specimen - of the production of the potato in 

 meal, flour, etc.,, and gave the following results of analysis : 



Starch. Gluten. Oil. 



Ib. lb. Ib. 



Components of the potato per cwt. 84-077 14-818 1-104 



Do. of wheat 78-199 17-533 4265 



