580 Dr. Schaf haeiitl on the Different Species of 



little. By actual analysis, a considerable quantity of carbon 

 was found in it, as well as arsenic, but 7io trace of' silicon. In 

 the retort, treated with hydrochloric acid as usual, the evolu- 

 tion of gas lasted upwards of three weeks : the evolved gas 

 had 710 smelly which proves that carbon, at least alone^ cannot 

 be the cause of the bad smell of this description of hydrogen. 

 The residuum of the solution was black, smoking very much 

 during ignition, and leaving a small quantity of dirty red re- 

 siduum, which was entirely soluble in hydrochloric acid, 

 leaving only a few small black scales behind. The solution 

 contained iron, but no traces of silica. 



I must here mention a fact but little known, that all piles of 

 iron which are to be welded in a reverberating- furnace, must 

 rest on a bottom which contains a large quantity of free silica. 

 When the pile of iron is heated in such a reverberating-furnace, 

 the silicon and the iron on the surface of the pile become 

 oxidized, forming a very tough half-melted slag, which does 

 not at all prevent the access of air, and the iron would burn 

 into cinders did not the silica of the bottom combine with the 

 slag next to it, forming a liquid silicate and giving an equal 

 (juantity of silica to the uppermost bar of iron in the pile, un- 

 til this liquid slag is spreail over the whole pile and its inter- 

 stices. Iron piles heated upon a slag bottom will not weld 

 but burn, a circumstance which I found always overlooked. 



When iron is heated on a bottom composed of siliceous 

 matter, for a long time and at the highest degree of heat, the 

 silicon of the bottom is reduced by the carbon of the iron as 

 well as of that of the flames, and combining with the iron ren- 

 ders its texture loose, makes it finally melt, and produces that 

 which is usually termed burnt iron. 



The silicon is, in fact, the cause of the welding property of 

 the iron. Thus silica is sometimes the cause of malleable 

 iron melting in our common fires. The general idea, that 

 malleable iron can be melted even in Sefstroem's or Knight's 

 blast-furnace, is quite erroneous. An accurate analysis of the 

 iron before and after fusion will soon convince us of the truth 

 of this assertion, and we find invariably that the iron during 

 fusion had combined either with carbon, or with silicon, or 

 with both. We have seen above, that iron, even though it 

 contains a large quantity of carbon, sometimes developes a 

 perfectly inodorous hydrogen, and an inodorous hydrogen is 

 therefore no proof of chemically pure iron. The process of 

 welding iron consists in heating the skeleton grains of iron, 

 contained in the mass, in order to excite all their attractive 

 forces, but at the same time to prevent their combining with 

 any other body, especially carbon, in which case only the 



