226 ANNUAL OF SCIENTIFIC DISCOVERY. 



posed by water. Its proper solvent is a concentrated solution of nitrate of 

 silver. It may be obtained in regular crystals. Photographic silver baths 

 which have been for some time in use always contain a portion of this com- 

 pound, the reason of their superiority to those more recently prepared. 

 Chloride and bromide of silver do not yield similar double salts, which ex- 

 plains why negative photographs on bromide of silver alone are deficient in 

 intensity. 



SPONGY METALS. 



M. Chenot has often remarked that in compressing spongy iron, the pro- 

 duction of a harsh sound accompanied the rupture of the molds employed. 

 Very recently, in compressing spongy silicium, this fact was reproduced hi a 

 very marked manner. Three gram's of silicium in the spongy state having 

 been submitted to a pressure equal to 300 atmospheres, it exploded with a 

 fearful noise the fragments of steel from the broken matrix, entered many 

 millimeters into a plate of cast iron, and the body of the hydraulic press, 

 which was 20 centimeters in thickness, was broken, and this although the 

 safety valve was open, thus showing the sudden violence of the shock. The 

 action was entirely from above, downward, since no portion of the upper part 

 of the compressed metal in this case suffered. 



ON THE DETECTION OF MANGANESE. 



The following paper has been read before the Eoyal (English) Society by 

 Edmund Davy, Esq. : 



Manganese is chiefly found combined with oxygen, but its oxyds are com- 

 monly mixed with those of iron, and though different methods of separating 

 them have been recommended, yet no very simple or unobjectionable test for 

 manganese seems to be known. Two methods for detecting manganese are 

 recommended viz., 1. The pure hydrated fixed alkalies, potash and soda, 

 and especially potash. 2. Sulphur. With regard to the first method. Though 

 the compound chameleon mineral, made by strongly heating niter or potash 

 and peroxide of manganese together, has long been known, yet it appears 

 hitherto to have escaped observation that potash seems to be a more delicate 

 test of manganese than any other known substance. The use of potash in 

 this way is simple and easy ; it is employed in solution ; equal weights of the 

 alkali and water form a fluid well adapted for the purpose ; different metals 

 may be used in the form of slips on which to make experiments, but a prefer- 

 ence is given to silver foil, as it is loss acted <}n by alkalies than platina, and 

 is more readily cleaned. A slip of such foil, about two or three inches in 

 length and half an inch wide, answers well. Solids, to be examined for 

 manganese, are finely pulverized ; fluids require no preparation ; the smallest 

 portion of ether is mixed with a drop or part of a drop of the alkali on the 

 foil and heated by a spirit-lamp (for many experiments a candle affords sufficient 

 heat), when on boiling the alkali to dryness and raising the heat, the charac- 

 teristic green mangauate of potash will appear on the foil. The delicacy of 

 the alkali as a test thus applied will be obvious on using the most minute por- 



