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ing the molten iron containing the carbon dissolved in it. The 

 mass was subjected to the action of acids which dissolved away 

 the iron and a few minute diamond crystals were found in the 

 insoluble residue. These were mostly of microscopic size but 

 answered every test for diamond and were as, truly real diamonds 

 as any that were found' in nature. Although the experiments have 

 been repeated with various modifications by several chemists it 

 has not yet been found possible to make diamonds big enough to 

 be of any commercial value. 



Graphite is another form of crystallised carbon. It differs 

 from diamond in many ways. It is soft instead of hard, black 

 and opaque instead of colourless and transparent, much less dense 

 (specific gravity about 2 i-5th), and a fairly good conductor of 

 heat and electricity. It occurs in nature and can also be prepared 

 artificially. It was formerly supposed to be a compound or a 

 peculiar variety of lead, hence the names black-lead and plum- 

 bago by which it is still often known. 



Amorphous carbon can be obtained in many ways and it is 

 not known for certain whether there are more than one and, if 

 so, how many, chemically distinct modifications of this substance. 

 Its physical properties certainly differ considerably according to 

 the source and method of production. 



When wood is heated so that air is excluded a number of 

 gases and vapours are evolved and a residue remains, black, 

 infusible, and insoluble, known as wood charcoal. An account of 

 the many uses of this and of the way in which it is prepared will 

 be given in a subsequent lecture, but I may mention here its power 

 of absorbing or occluding gases. As a general rule the gases that 

 are easily liquefied are absorbed to a larger extent than those 

 which are difficult to liquefy and the absorbent power of the 

 charcoal is different according to its source. For example, that 

 made from cocoa-nut shell is specially active in this respect. 

 Charcoal, or a similar form of amorphous carbon, may be obtained 

 by the action of concentrated sulphuric acid upon various organc 

 substances, the most suitable of these being sugar. By heating 

 animal matter such as flesh, dried blood, or bones, animal char- 

 coal is produced. As in the case of wood charcoal, air must be 

 excluded during the heating process or the charcoal would itself 

 be burnt. This kind of charcoal is particularly useful /for the 

 absorption of colouring matters. 



I have already said that diamond, graphite and charcoal, 

 when burnt in oxygen, give the same product, namely, carbonic 

 ac ! d gas, and that equal weights of this gas, and no other sub- 

 stance whatever, are produced when equal weights of the three 

 forms of carbon are burnt. It is also possible to convert diamond 

 into graphite by powerful heat in the absence of air, and the 

 conversion of charcoal into diamond, as in Moissan's experiments, 

 completes the series of transformations. Thus it is beyond doubt 

 that the three substances are, at bottom, identical in nature. 



The existence of a smgle element in two or more allotropic 



