i8yi.] Chemical Science. 551 



When solid nitrate of silver, either in crystals or sticks, is placed upon 

 glowing charcoal, deflagration takes place, the silver being left in the metallic 

 state, while binoxide of nitrogen and carbonic acid are evolved. The nitrate 

 is fused by the heat of the reaction and sinks into the pores of the charcoal, and 

 as each particle of charcoal is replaced by metallic silver, the structure of the 

 original wood is preserved. With proper management, pieces of silver of any 

 desired size can be prepared, showing the exact structure of the wood. Dr. 

 Chandler recommends that a crystal of nitrate be placed on the end of a piece 

 of charcoal, and the blowpipe flame directed upon the coal near the crystal to 

 start the reaction. When deflagration begins, crystal after crystal may be 

 added. The nitrate fuses, passes down through the porous metal already 

 reduced until it reaches the glowing coal, where it is reduced. Lumps of silver 

 weighing an ounce or more, which exhibit most beautifully the rings of 

 the wood, have been prepared in this manner. 



The behaviour of arsenic acid with hydrochloric acid, with a view to ob- 

 taining an acid free from arsenic, has been examined by J. Mayrhofer. His 

 paper contains the record of the results of some experiments made with the 

 view to ascertain under what conditions and in what state of combination 

 arsenic is carried over by the distillation of hydrochloric acid which is con- 

 taminated with arsenic. It appears that the degree of concentration of the 

 last-named acid, and the relative proportion of arsenic acid present, and also 

 the care taken in cautiously distilling, are of influence in obtaining an arsenic- 

 free distillate; but, moreover, the treatment of the hydrochloric acid with 

 chlorine, or, better still, with sulphuretted hydrogen, previous to distillation, 

 to be next carefully conducted, will ensure the distillate being free from arsenic. 



In some recent experiments in chemical dynamics, Dr. J. H. Gladstone, 

 F.R.S., and Alfred Tribe, F.C.S. had occasion to study the action of nitrate 

 of silver on copper plates in various positions. They observed that, when 

 the plate was vertical, there was rather more corrosion at the bottom than at 

 the top. This is easily accounted for by the upward current, which flows 

 along the surface of the deposited crystals, and which necessitates a movement 

 of the nitrate of silver solution towards the copper plate, especially impinging 

 on the lower part. It was also found that, when the copper plate was varnished 

 on one side, it produced rather more than half the previous decomposition, 

 and was most corroded at the edges of the varnish. By making patterns with 

 varnish, this edge action became very evident. This was explained by the fact 

 that the long crystals of silver growing out from the copper at the borders can 

 spread their branches into the open space at the side, and so draw their supply from 

 a larger mass of solution than the crystals in the middle can do; and increasd 

 crystallisation of silver means increased solution of copper. This was proved 

 by making the varnish a perpendicular wall instead of a thin layer, when the 

 greater corrosion was not obtained. In a plate completely surrounded with 

 liquid, the greatest growth of crystals is also evidently from the angles. It 

 was likewise observed that, if a vertical plate be immersed, the lower part in 

 nitrate of copper and the upper part in nitrate of silver, there is greater 

 corrosion about the point of junction ; this was attributed to the greater con- 

 duction of the stronger liquid. 



A new precipitating reagent for copper has been proposed by Mr. Hugo Tamm, 

 which promises to be of great service in analysis. Such a reagent, to be 

 perfect, must fulfil certain conditions. (i). When employed for the deter- 

 mination of a solid substance it should be volatile, or, if it is fixed, it should 

 not form, with the precipitate, compounds of indefinite composition. (2). It 

 should form, with the element to be determined, a compound as insoluble as 

 possible. (3). It should not introduce in the liquid separated from the pre- 

 cipitate any substance likely to alter the behaviour of its constituents, with 

 general or respective reagents, and, least of all, it should not introduce any 

 substance difficult of separation from any of the constituents. (4). It should 

 separate the element to be determined, in the shape of a compact precipitate, 

 in neutral or acid liquors, and allow the other elements of the combination to 

 remain in solution. This is, perhaps, the most important principle in 

 analytical chemistry. The reagent which Mr. Tamm proposes for copper 



