CHEMICAL SCIENCE. 195 



chloride of' potassium and sodium. These ingredients are mixed 

 together dry, placed in a clay crucible, and quickly heated to red- 

 ness. When the mass is fused the crucible is withdrawn from the 

 furnace, broken, and the slag removed. This slag serves, by reason 

 of the silicide of magnesium which it contains, for the preparation 

 of the desired gas. It is necessary to break up the slag into frag- 

 ments, and act upon them under water with strong hydrochloric 

 acid. The gas, the composition of which seems to be Si 2 H 4 , is at 

 once liberated, and may be collected over water or mercury. If a 

 bubble of the gas be allowed to escape into the air, it bursts into 

 flame with explosive violence, a white, hollow, cylindrical ring of 

 smoke ascends, rotating, undulating, and widening as it goes up, and 

 distributing, when it breaks, a multitude of fine flakes of dry silica. 

 All the appearances noticed remind the spectator forcibly of the 

 phosphuretted hydrogen, but there is no offensive smell produced. 

 When the gas is left long in contact with water, the curious hydrated 

 oxide is formed, to which we have already alluded. This substance 

 is white, and when dried and heated in a tube scintillates just like 

 the analogous substance obtained by the oxidation of graphite. 

 This oxide of silicon has the formula SLH 2 O . 



ARTIFICIAL PLUMBAGO. 



For some time past, Dr. Grace Calvert, F. R. S., has been engaged 

 in experimenting upon the composition of a carboniferous substance 

 existing in gray cast iron, or, to use a more, popular definition, in pro- 

 ducing plumbago from cast iron. The effect of his experiments has 

 been to arrive at results which throw much light upon the chemical 

 composition of the substance, proving it to be composed of iron, car- 

 bon, nitrogen, and silicium. The substance occupies exactly the 

 same volume as the cast iron from which it is obtained, and is suffi- 

 ciently soft to be easily penetrated by a blade. The mode of experi- 

 menting pursued by Dr. Calvert consisted in placing cubes of Staf- 

 fordshire cold-blast cast iron in corked bottles, with eighty times their 

 volume of weak solutions of the following acids : Sulphuric, nitric, 

 hydrochloric, acetic, oxalic, tartaric, and gallic. Besides these, phos- 

 phoric, carbonic, oleic acids, tannin, and acid peat-water, were also 

 used. After three months of contact, he found that although the 

 external appearance of the cubes was not changed in any of the ves- 

 sels, still those in contact with the weak sulphuric, hydrochloric, and 

 acetic acid solutions, especially the latter, had become so soft exter- 

 nally that the blade could penetrate three or four millimetres into the 

 cubes. He therefore removed the solutions from the vessels, and 

 replaced them by an equal bulk of each weak acid solution, and con- 

 tinued to do so every month for two years, at the end of which time 

 the cubes in contact with the acetic acid ceased to yield iron to the 

 acid, although they were still of the original size ; they had, there- 

 fore, become transformed into the carbonaceous substance, or artifi- 

 cial plumbago. The action of the weak acetic acid solution Dr. 

 Calvert found to be complete, that of the hydrochloric and sulphuric 

 solutions nearly so, and that of the nitric much less complete, whilst 

 the other solutions either showed no similar action, or a very slight 



