00 

 Oh> 



THE COMPRESSIBILITY OF CARBON, SILICON, 



being recorded in the second column of figures. A small weighed globule 

 of mercury was now added, and pressure was again applied. The weight 

 added and the new pressure are recorded in the third column. In the same 

 way the fourth and fifth columns of figures were found. From all these 

 values, with the help of a plotted curve drawn through the points which 

 they represent, were computed the values given in the sixth column of 

 figures, headed W . This records the amount of added mercury needed 

 by each jacket to cover the range of pressure from 100 to 500 kg. per 

 square centimeter. Each jacket must have this series of experiments 

 carefully made with it, on account of the variations in the compressibility 

 of glass- The figures given for jacket v are merely a repetition of those 

 given in somewhat different arrangement in a previous table. 



In compressing an irregularly shaped sub- 

 stance, such as a mass of broken pieces, or a 

 quantity of crystals, beneath the mercury in 

 one of these jackets, errors are liable to arise 



because the surface tension 

 of the mercury keeps this 

 liquid out of the finest 

 cracks and cavities. Hence, 

 unless further precaution is taken, 

 the observed values for the com- 

 pressibilities are always larger 

 than the true ones. We have found 

 this difficulty may be wholly over- 

 come if the solid is first thoroughly 

 surrounded by a liquid which wets 

 it, the major part of this liquid 

 being subsequently displaced by mercury in 

 case the metal is without action on the solid. 

 The film of lighter liquid wholly surrounds 

 the solid, and is everywhere also in imme- 

 diate contact with the mercury, so that no 

 empty spaces are left. 



In order to compute the results from 

 data thus obtained with three substances in 

 A f the jacket, the compressibility of the lighter 



p: 5 Jacket III. Fig. 6. Apparatus for 



Powders. liquid, as well as the quantity present, must 



be exactly known, just as in the case of the alkali metals which has already 



been discussed. 



As water was the supplementary liquid most convenient to use in 1 

 present case, pains were taken to determine accurately its compressibility 



