338 ANNUAL OF SCIENTIFIC DISCOVERY. 



. 

 the action of salt in increasing the fertility of certain lands. We have not 



space for details, but quote Mr. Northcote's conclusions*: " The results, 

 then, at which we must arrive arc, that agricultural salt is a most energetic 

 absorbent of ammonia, botii in virtue of its chloride of sodium and of its 

 soluble lime-salt, and that the proportion of the latter especially most power- 

 full}- affects its action ; but that at the same time its agency does not seem to 

 be altogether a permanent one ; it Avill collect the ammonia, but it is ques- 

 tionable whether it can retain it for any great length of time, because in the 

 very decompositions which happen in order to render the ammonia more 

 stable, salts arc formed which have a direct tendency to liberate ammonia 

 from its more fixed combinations. It may, however, retain it quite long 

 enough for agricultural purposes ; if the young plants are there ready to re- 

 ceive it, its state of gradual liberation may be for them the most advanta- 

 geous possible ; and to this conclusion all experiments on the large scale 

 appear most obviously to tend. It is described as an excellent check to the 

 too forcing power of guano ; and from M. Barral's experiment we sec that it 

 either prevents the too rapid ercmacausis of the latter, or stores up the am- 

 monia as it is formed. As a manure for growing crops, all experience and 

 all theoretical considerations therefore show it to be most valuable ; but 

 when employed to mix with manure heaps which have to stand for consider- 

 able periods of time, theory would pronounce, as practice has in many cases 

 done, that its power of retaining ammonia under those circumstances is at 

 the best doubtful." 



NOTES ON ALU3I IN BREAD AND ITS DETECTION. 



At a recent meeting of the London Chemical Society, a paper was read 

 by Mr. Iladow, upon the above subject. 



After detailing two processes which have been put forward for the examin- 

 ation of bread for alum, Mr. Hadow stated that, wishing to test these pro- 

 cesses, lie had a loaf prepared by a baker, into the dough of which had been 

 put the large quantity of eighty grains to the quartern loaf. After baking, 

 the loaf was broken into pieces, and macerated with successive quantities of 

 water, and the whole afterwards filtered ; a clear liquid was obtained, a por- 

 tion of which was tested with chloride of barium and witli ammonia, and a 

 precipitate obtained in each case. The remainder of the liquid was evapo- 

 rated to dryncss, and the residue, ignited to burn off any organic matter, 

 was dissolved entirely by water and dilute nitric acid. Pure potash added 

 to this solution gave a dense precipitate, insoluble in an excess of the pot- 

 ash. The filtered liquid from this precipitate, after the addition of chloride 

 of ammonium in excess, remained perfectly clear, showing the total absence 

 of alumina. 



The bread, after maceration, was incinerated, and the ash dissolved in 

 dilute nitric acid, and the solution treated with pure potash in excess, a pre- 

 cipitate was left, which wa* removed on a filter, and the filtered liquid 

 on addition of chloride of ammonium gave a large precipitate of alumina. 



From these results it will be seen that macerating the bread in water does 

 not dissolve out any alum from it, and that from any experiments made in 



