114 SYSTEMATIC DESCRIFITON OF PRECIOUS STONES 



meaning of its apparent destruction when exposed to heat were undertaken later by the 

 famous French chemist, Lavoisier, as well as by Tennant, Davy and othei's. 



During the year 1772 and later, Lavoisier, the founder of modern chemistry, demon- 

 strated that the disappearance of diamond only took place when it was heated in air, and 

 that it might be exposed to the highest temperatures without loss of weight, provided that 

 any contact with air was prevented. He further showed that the air occupying the space 

 in which a diamond had been heated, and in which it had finally disappeared, possessed the 

 property of turning lime-water milky, as does carbon dioxide (carbonic acid gas) ; and, 

 moreover, that the lime-water so clouded effervesced when brought into contact with an 

 acid, just as it does when clouded by the addition of carbon dioxide. The consideration of 

 these facts led him to repeat his experiments, replacing diamond with ordinary carbon ; the 

 results were found to be identical, and there was nothing for it but to conclude that the 

 disappearance of diamond was due to combustion. In spite of these apparently conclusive 

 experiments, Lavoisier did not at that time venture to assert that the substance of carbon 

 and of diamond was completely identical. 



This was left to be proved by Smithson Tennant, who in 1797 demonstrated that 

 the combustion of a certain weight of diamond resulted in the production of the same 

 amount of carbon dioxide as did the combustion of an equal weight of pure carbon. This 

 observation was confirmed later by other chemists, for example by Sir Humphry Davy, who 

 in 1816 showed in addition that the combustion of diamond was imattended by the formation 

 of even a trace of water. This proved that the conclusions of Arago and Biot, namely, 

 that diamond, on account of its high refractive power, must contain a hydrocarbon, were 

 incorrect. Later, all these results were confirmed by the well-arranged experiments of 

 Dumas and Stas, as well as of Erdmann and Marchand, and others. The combustion of 

 diamond in oxygen gas has now long been an every-day chemical lecture experiment. 



These researches have been considered for some time to have finally settled the question 

 as to the constitution of diamond. Recently, however, Krause has suggested that this 

 question should rather be regarded as still an open one, and that the experiments which 

 have been described should be taken to prove simply that the atomic weight of the element 

 of which diamond is composed is identical with that of carbon. He has further suggested 

 that between the two, diamond and ordinary carbon, there might possibly be a relation 

 similar to that existing between the metals nickel and cobalt, which have the same, or very 

 nearly the same, atomic weight and very similar chemical characters. In order to decide 

 this point, Krause allowed the gases produced on the one hand by the combustion of 

 diamond, and on the other by that of pure carbon, to be absorbed by caustic soda. In 

 both cases he obtained crystals : in the one case these were, of course, crystals of sodium 

 carbonate ; in the other, the crystals produced agreed so completely with the crystals of 

 sodium carbonate in crystalline form, amount of water of crystallisation, specific gravity, 

 fusibility, solubility, electrical conductivity, &c., that there could be no reasonable doubt of 

 the identity of the two products. This experiment, then, proves definitely and conclusively 

 that the product of combustion of diamond is carbon dioxide, and that the substance of 

 diamond consists, therefore, of pure carbon. 



A century previous to the work of Krause, Guyton de Morveau had made experiments 

 with the idea of confirming or overthrowing the results of Lavoisier and Tennant, thinking 

 it inconceivable, as did the majority of his contemporaries, that the rare and costly diamond 

 and a common and widespread substance^ such as carbon could consist of one and the same 

 chemical element. The method he adopted for the purpose differs from the usual methods of 

 chemical analysis, and is interesting on account of its originality. It depends on the fact 



