-30 THE COMPRESSIBILITY OF CARBON, SILICON, 



able to secure enough colored diamonds free from mechanical defects to 

 obtain adequate measurements. The commercial value of 20 grams of 

 colorless perfect diamonds is so great that it was questionable if the results 

 would be commensurate with the risk involved. Accordingly, these were 

 not used, although kindly offered. Nevertheless, it is hoped that, before 

 long, enough suitable crystallized carbon may be obtained to complete the 

 study of this subject. 



Silicon was very kindly furnished in quantity by Mr. F. J. Tone, of the 

 International Atcheson Graphite Company at Niagara Falls. The sub- 

 stance was in a compact brilliant crystalline mass, free from cracks or gas- 

 holes, very suitable for the purpose in hand. Before use it was broken 

 into small pieces fit for introduction into the jacket. In two experiments, 

 1.346 and 4.464 grams of the substance lost, respectively, 0.558 gram and 

 1.837 grams on immersion in water, corresponding to specific gravities of 

 2.41 and 2.43, respectively. The average, 2.42 (20/20), lies between 

 the values found by Wohler and by Winkler. The true density, corrected 

 to the vacuum standard, is essentially the same. In the case of very slightly 

 compressible substances like this the knowledge of the specific gravity of 

 the sample within 1 per cent is very important. 



The carbide of silicon (''carborundum"), also made by the same firm, 

 was studied. Large masses of crystals of this substance were gently frac- 

 tured in order to open existing cracks without starting new ones. Its 

 specific gravity was 3.20 (20/20), as 6.277 grams displaced 1.988 grams 

 of water; hence its density was 3.19. 



Sulphur was investigated in its densest form clear crystallized rhom- 

 bic sulphur having a specific gravity of 2.07. The other forms are too 

 unstable under pressure to give satisfactory results. A very pure sample 

 Avas obtained, which contained only negligible amounts of other substances. 



Selenium, in a state of adequate but not perfect purity, was obtained 

 from a well-known German firm, in small fragments. These were broken 

 into somewhat smaller pieces in order to open accidental cavities. Of this 

 material 8.959 grams were found to displace 2.0946 grams of water at 20, 

 indicating a specific gravity of 4.28 (20/20), a figure identical with the 

 value found by Saunders.* 



Red phosphorus was treated several times with carbon bisulphide to 

 remove any yellow phosphorus which might be present, and the last traces 

 of the liquid were evaporated. 



Mercury was carefully purified as usual. Ordinary distilled water is 

 pure enough to play the role required of it. Thus all the substances were 

 prepared for compression. 



*Journ. Phys. Chem., 4, 491 (1900). 



