M. Karsten on the Carbon in Iron and Steel. 291 



tion. The residuum contains carbon in a state different from 

 the graphite: but gray raw iron can never be dissolved in 

 muriatic acid without leaving it. Strong sulphuric acid, em- 

 ployed under similar circumstances, leaves, besides the gra- 

 phite, black carbon easily combustible and not subject to the 

 magnetic attraction. 



Nitric acid of specific gravity 1-3 does not operate strongly 

 on gray raw iron at common temperatures. At the same time 

 effects are produced which appear to coincide, sometimes with 

 those exhibited by hard steel, and sometimes with those cha- 

 racteristic of soft steel. The former appear in the darkest and 

 softest and most ductile gray raw iron, and the latter in the 

 lighter coloured and at the same time less soft and ductile 

 kind of this metal. The action of the acid appears to be in- 

 terrupted ; for the solution seems to cease from time to time 

 entirely, but re-appears with great violence on the breaking off 

 of a leaf of graphite. The same appearance takes place in a 

 boiling temperature; and the violent progress of the solution — 

 which however only lasts for a few seconds — is combined with 

 the falling off of a leaf of graphite : so that the graphite must 

 actually form a mechanical impediment, protecting the iron 

 against the attacks of the acid, and rendering the solution 

 so difficult, that at common temperatures it is only affected in 

 several weeks ; and at a boiUng heat, in several hours. The 

 colouring of the acid proves that part of the carbon contained 

 in the iron is dissolved : the residuum seldom consists of pure 

 graphite, but mostly of graphite with more or less of carbon 

 changed into a brown powder. 



In order to explain these appearances attending the solution 

 of different kinds of iron in acids, it is necessary to find out 

 the nature of the substances which separate during the process 

 of solution. The graphite being insoluble in acids and alka- 

 lies, may be stated to be quite pure. In a strong red-heat and 

 exposed to the atmosphere it is volatilized slowly, without 

 leaving any residuum. In order to volatilize 18 grains of gra- 

 phite under the muffle of an assaying-furnace four hours were 

 required, although the muffle was kept during the whole time 

 at a white heat. This rather considerable quantity of graphite 

 left on the platinum plate, on which it had been spread in 

 order to give the heated air a greater scope for action, only a 

 trace of silica, perfectly white, which had escaped the effect 

 of the alkaline solution. In this process of combustion the 

 graphite gradually decreases in bulk, and disappears at last 

 without any kind of flame being perceptible. If the process 

 be interrupted, the only difference seen between the part of 

 the graphite calcined and that which is not, is, tliat the leaves 

 O o 2 of 



