THE COMPRESSIBILITY OF CARBON, SILICON, PHOSPHORUS, 



SULPHUR, AND SELENIUM. 



INTRODUCTION. 



The preceding paper upon the alkali metals led to the conclusion that 

 among similar elements large atomic volume is at least occasionally asso- 

 ciated with great compressibility. Inspection of the figures for other sub- 

 stances quickly indicates that atomic volume is not the only property which 

 thus takes part in determining the magnitude of the effect of pressure ; but 

 clearly there is some connection between the two properties. Therefore it 

 seemed probable that elements possessing small atomic volume must pos- 

 sess slight compressibility; and with a view to subjecting the hypothesis 

 to a striking test, carbon and silicon, which lie in the first two valleys of the 

 atomic- volume curve of Lothar Meyer, were subjected to experimental 

 investigation. Having found in the results with these elements a vindica- 

 tion of the hypothesis, other non-metals with larger atomic volume, namely, 

 sulphur and selenium, were studied in order to obtain further light upon 

 this relation and other possible modifying circumstances. In a previous 

 research,* the compressibility of yellow phosphorus was determined ; it 

 was now desired to determine if the more dense modification, red phos- 

 phorus, has the smaller compressibility which would be expected of the 

 more compact material. Therefore red phosphorus also was studied, with 

 interesting results. 



The method of investigation was essentially similar to that employed in 

 the case of the alkali metals, the substances being compressed under a neu- 

 tral liquid in a suitable glass jacket, the extent of the compression being 

 determined by the weights of mercury needed to make contact with a fine 

 platinum point at various pressures. Due correction was of course applied 

 for the contraction of the jacket and the liquids, in the simple manner 

 already indicated. 



PREPARATION OF MATERIAL. 



Several samples of carbon were employed, including charcoal of various 

 kinds, and both natural and artificial graphite. Effort was made to secure 

 diamonds, also, but although Mr. George F. Kunz, of Tiffany & Co., New 

 York, has kindly interested himself in the matter, we have not yet been 



*Richards and Stull, Carnegie Institution of Washington Pub. No. 7. 



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