CHEMICAL SCIENCE. 273 



assumed that the illuminating effect of the gas is diminished by a loss of the 

 carbon contained in the olefiant gas, to which a large part of the light-giv- 

 ing quality has been attributed. It becomes an interesting point in general 

 chemical science, to learn how far the facts gained by observation and ex- 

 periment will sustain these assumptions which have been held in relation to 

 the source of gas-carbon as above alluded to, and to inquire into its connec- 

 tions more particularly. Gas carbon, in its difficult combustibility under a 

 current of heated air, its relation to nitrates of the alkalies and sulphuric 

 acid, must be classed with the carbon found in crude iron, and called 

 graphitic carbon, or carbon in an allotropic state. It differs as much from 

 lampblack and charcoal as these do from diamond, and in the artificial pro- 

 duction of it, in all the cases hitherto observed, it has a certain relation to 

 vapors. The fine specimens obtained when molten iron passes over moist 

 earth, the metallic-like glazing of coke, and the lustrous residues of animal 

 decomposition by heat, in presence of vapors, are all instances of the exist- 

 ing connection between vapors and this allotropic carbon. 



" Taking a suite of specimens, the microscope enables us to see, in the 

 early stages of deposition, that every part is vesicular; that mammillary 

 forms result from the aggregation of the vesicles ; and, pursuing these ob- 

 servations, we often find the broken vesicles filling vacant spaces between 

 those more perfect, and a consolidation resulting from this arrangement. 

 "Where pendent parts exist, their sections show a perfectly regular building 

 up from layers of sublimate, each layer being composed of vesicles, more or 

 less broken ; the thin shell of each exhibiting the superposition of layers 

 which belongs to bubbles. The examination of hundreds of specimens will 

 not show any departure from this character of a sublimate, produced cither 

 from its own vapor, or when transported by another kind of vapor. Y> r e 

 find also that those coal carbo-hydrogcns which afford most vapors are those 

 which leave in their decomposition most allotropic carbon ; the natural bitu- 

 mens affording the most remarkable and convincing results in this way, 



" As the mechanical state of the gas carbon, clearly shown under the 

 microscope, as well as to the unassisted eye, is that of a solid left from a 

 transporting vapor, observation indicates that it has been thus formed in the 

 very compound atmosphere resulting from coal decomposition. It is a fact 

 of chemical science, that olefiant gas, when heated, deposits carbon, and the 

 fact can be easily demonstrated. But it is a remarkable feature in this de- 

 composition, that the gas deposits its carbon in the form of lampblack, and 

 the utmost reach of the means of control will not produce an aggregation 

 of particles resembling charcoal. In high or comparatively low tempera- 

 tures, the deposition never has the state of allotropic carbon, and, chemically 

 speaking, there is no evidence that this form of carbon can result from olefiant yas 

 changes. If, however, vapors of bitumen arc mixed with the olefiant gas, 

 these vapors suffer decomposition by heat, and we easily obtain in the mix. 

 ture vesicular brilliant carbon in the allotropic state of gas carbon ; while 

 the vapors solely much more readily afford this substance, in form arid com- 

 position closely resembling gas carbon. 



" The subject, as I have studied it, appeared to possess interest in connec- 



