248 An Attempt to analyie Cast Iran. 



tlon with nitric acitl alone, and from that with nitro-mn* 

 Tiatic acid, there ultimately remained a black-brown, soft, 

 carbonaceous mass, which in its appearance was perlectly 

 alike from different experiments; but varied much in che- 

 mical habitudes, according to the quantity and concentra- 

 tion ot" tlie acid, the temperature at the dissolution, and 

 other circumstances. It amounted on an average to more 

 than 4 per cent. oF the weis;ht oF the iron employed. It 

 was alvvavs in a small deoree soluble in water, and in its 

 chemical character lesemblcd the extractive substance mei 

 with in mould earth — the last staae oF vegetable putrefac- 

 tion. In some experiments, I found it so soluble in boiling 

 water, that on cooling a great quantity was again precipi- 

 tated ; caustic aunnonia dissolved it more copiously thaa 

 water. In other experiments, it was less soluble in water, 

 but then proportionably more so in caustic alkali, with 

 which it Formed a dark, opake, and neaily black fluid, 

 which, like the alkalitie solution of the extractive substance 

 before mentioned, was again precipitated by acids. IFaa 

 aquLous solution oF this brown substance be evaporated, it 

 then precipitates, and the liquor gradually loses its colour. 

 On heating this substance, it smelt like heated peat turf^ 

 and when inflam'jd it spontaneously continued in a state 

 of ignition, giving a smell of peat ; after which there re- 

 mained aravish-red ashes. In short, the action of the 

 nitric acid on the caibon of the cast iron generates here a 

 substance, which in character is identical with the extractive 

 substance from mould earth and peat turf. 1 do not intro- 

 duce this as an essential circumstance relative to the corn- 

 position of cast iron, but as a remarkable phaenomenon of 

 the action of nitric acid on carbon, which perhaps might be 

 classed along with Hatchett's discovery of artificial tannin, 

 from the mutual action of charcoal and nitric acid. A 

 part of this extractive substance dissolves in the last water 

 of edulcora'.ion, and therefore it has passed into the so- 

 lution of iron undissolved. If this be precipitated with 

 caustic ammonia, then the reiiiaining solution is sometimes 

 yellow ; this substance dots, however, for the most part 

 precipitate with oxide of iron. When this is digested 

 with caustic potash the lev will be of a dark-brown colour, 

 though none of the oxide of iron is dissolved. These cir- 

 cumstances are sufficient to show the impossibility of de- 

 termining the quantity of carbon by the solution of iron in 

 nitric acid. 



I noticed a constant peculiarity of this extractive Sub- 

 stance, that though digested with diluted muriatic acid, so 



tha^ 



