VARIATIONS OK SPKCIFK^ (JHAVITY. 263 



wliicli nw too soft —lead, i'oi" cxaiiiplc — Iimnc (oo litllc cohesion, itiid 

 are toni in iUtompliuii,' to draw them into wii'cs. 



In tlie ])rot'('ss of wire drawiiiii; tiic metals arc then in fact com- 

 pressed, and in accof(hincc Avith wlial has hccn said, a certain dim- 

 inution of density is to he expected if the pressure is hi<2^h enou<ih, 

 hut thei'e arc no cei-tain grounds to jnvdict what miglit ha[)pen in 

 furthc r continuation of the process. 



1 had formerly found advantage in the use of the pyknometer, in- 

 stead of the Archimedean method of detei-mining specific gravity, 

 hut had found an improvement in the lattei" when the supporting 

 Avire is carefully platinized. Bv the friendly advice of Dr. Ch. Ed. 

 Guillaume and Dr. V. Chappius, both of the Bureau International 

 des Poids et Mesurcs in Pavilion de Breteuil in Sevres, who have 

 been good enough to impart to me and my colleague the approved 

 method employed at that institution, Ave liaA'e been able to avoid com- 

 pletely the error formerly encountered, and have employed the 

 method of displacement, Avith the same success Ave had previously 

 obtained by the pyknometer. 



I give here only a small part of the results obtained, and choose 

 for the purpose of illustration the experiments Avith platinum. It is 

 not only a duty but a privilege to acknowledge in this connection the 

 uncommon goodness of the firm of AV. C. Heriius, in Hanau, Avho 

 have not only furnished me liberally Avith the costly material, but 

 also, to avoid error, have separately draAvn all the Avires required for 

 the research. 



Three parallel series of experiments Avere carried out, as folloAvs: 

 From a single bar of the IlerRus connnercial platinum pieces lying 

 side by side were cut off, and three cylinders, each about 6 mm. in 

 diameter and 35 mm. long. Avere turned to a uniform Aveight of 32 

 grams, then sent to us in Basel, Avhere Ave determined their s^pecific 

 gravity. We then returned the samples to Hanau, Avhere by rolling 

 and hanunering they Avere reduced to a diameter of 3 and length of 

 55 mm., suitable for Avire draAving. The specific gravity of these 

 samples was again measured in liasel. Returning them to Hanau, 

 they Avere drawn successively to Avires of 1, 0.7, and O.-i nnn. diameter. 

 After each draAving complete determination of the specific gravities 

 of these Avires was made in Basel, and they Avere then before further 

 draAving softened by heating to incandescence for three minutes. 

 But before being further drawn— the Avires Avere ahvays cold 

 drawn— the density of these softened Avires Avas determined, so that 

 we made 3 times 3 determinations on hai-d Avire and the sanu^ number 

 on soft Avire.* 



The results Avhich I noAV proceed to give are the mean of three re- 



oHere follow in the original article full details of a single determination, 

 from which the extreme care and accuracy of the work is apparent. 



