264 



VARIATIONS OF SPECIFIC GRAVITY. 



peated experiments with each of tlie three samples at each stage of 

 its treatment. These measurements were made without exception by 

 mv colleague, Mr. F. Sturm, and the mean error of the G9 deter- 

 minations has the extremely satisfactory value of only O.OOO-t, 



Table I.—Tiwned cylinders (I) and rolled dial hammered cylinders (II). 



I. Platinum cylinders. 



II. Platinum cylinders, rolled and hammered 



No. 1. 



21.2136 

 21.2137 

 21.2137 



21.2137 



21.4.317 

 21.4316 

 21.4308 



21. 4314 



No. 2. 



21.3061 

 21.3062 

 21.3057 



21.3060 



21.4192 

 21. 4190 

 21.4201 



21.4194 



No. 3. 



21.1.326 

 21.1323 

 21.1330 



21.1326 



21.4147 

 21.414.5 

 21.4140 



21. 4144 



These numbers confirm my earlier statement, and show that even 

 with such a favorable material as platinum the results are strongly 

 aflected by the individuality of the sample examined. Samples cut 

 from immediate proximity off the same bar show a difference of 

 density of O.lT^j-l. 



By rolling and hammering the density is increased by, roughly, 1 

 per cent, and the dift'erence of density between the three samples is 

 at the same time reduced to about one-tenth its former magnitude. 

 There is then nothing new in Table I, which merely proves the pres- 

 ence of pores or faults, which are diminished by the application of 

 mechanical force. 



Table II is, however, more interesting: 



Table II.— Rolled and hammered samples {II) and 1 mm. cold-drawn loire {III). 



11. Platinum samples, rolled and hammered 



III. Platinum wire 1 mm. in diameter, <'()ld drawn 



No. 1. 



21.4317 

 21.4316 

 21. 4308 



21.4314 



21.4139 

 21.41»i 

 21.4132 



21. 4136 



No. 2. 



21.4192 

 21.4190 

 21. 4201 



21.4194 



No. 3. 



21. 4147 

 21.4145 

 21.4140 



21.4144 



21.4232 

 21.4224 

 21.4223 



21.4229 

 21.42:34 

 2L4235 



21.4226 



21.4233 



Sample 1, which had the highest density as hammered platinum, 

 showed a diminution in specific gravity of 0.01T8, which is a difler- 

 ence far beyond the mean error of measurement (0.0004) already 

 given. Samples 2 and 3, which had been somewhat lower in density 

 than No. 1, advanced somewhat, but, as we shall see, it is probable 

 that behind this ajjparent increase a decrease is really hidden, and 

 that samples 2 and 3 also would have showed a falling off had they 



