310 



Through some uuexplaiued misconception, this per cent, of stretch is 

 called the elasticity, though it were more properlj^ styled the ductility 

 of the thread. Adopting, however, the consecrated usage, we shall 

 continue in these notes to use the term "elasticity" with this signiticauce. 



The elasticity of silk in its normal state is, as has been stated, from 

 15 per cent, to 20 per cent. Many conditions, however, may vary these 

 results within and even beyond these limits. One of the most impor- 

 tant of them is the amount of water contained in the silk. By the term 

 " normal state" I mean about the same as by "conditioned weight ; " 

 that is to say, its state in an atmosphere of moderate dryness. 



As au instance of the above I may cite the example of a thread which 

 in the normal state had rather less than the average elasticity, that is 

 to say, 14.7 per cent., which when thoroughly moistened only broke when 

 elongated 19.4 per cent. 



Among the more accurate of experiments on this subject are those 

 of M. Persoz. They may be summarized as follows: 



The presence of an excess of water in the silk exercises a notable 

 effect on its elasticity, and (according to this author) on its tenacity, 

 increasing the former and decreasing the latter. On the other hand, 

 silk reduced to absolute dryness loses slightly in tenacity, but very con- 

 siderably in elasticity. This is shown from the following experiment 

 upon a 1.62 gram* white reeled silk : 



It will be seen that between l!^os. 2 and 3 the tenacity has diminished 

 3.8 per cent., and the ductility 56.8 per cent., and that between Nos. 2 

 and 1 the ductility has increased 17.4 per cent. 



M. Francezou, who enjoys the reputation of being, from a scientific 

 point of view, the most talented silk reeler in France, has also made ex- 

 haustive experiments on the elasticity and tenacity of silk, and his con- 

 clusions are in some points different from those of MM. Kobiuet and 

 Persoz. Unfortunately, 1 have not been able to obtain his writings and 

 therefore am forced to derive my information of his work from second- 

 ary sources.! 



M. Francezou so improved the use of the serimeter as to compare, 

 with entire precision, silks differing in size and in hygrometric condition. 

 To evaluate the hygrometric condition during these tests, the skein to 



* That is to say, a silk weighing 1.62 grams per 500 meters. The weight in grams 

 of a skein of this length is the international standard for the sizing of silk adopted 

 by the congress of Brussels. — P. W. 



i Maillot— Z/fpons stir le Versa Sole de Murier, p. 205. 



