311 



be tested was wound upon a reel 1.250™ in perimeter and then cut 

 exactly into two equal parts; one of tbese halves was weighed at once, 

 and again after drying (absolutely), which gave the conditioned weight 

 sought, as well as the quantity of water contained before the tests ; the 

 other half served in part for the tests aud what remained was weighed 

 as it was, and again after drying, which gave the weight of water con*- 

 tained alter the tests ; the mean obtained from these weights was taken 

 as the average " hygrometric condition." 



As a result of these experiments M. Francezon differs from both the 

 authors already quoted by concluding that humidity has no effect on 

 the tenacity. In relation to the elasticity, however, he has found where 

 the silk contains not less than 8 per cent, and not more than 11 per 

 cent, of water a variation of 1 per cent, of moisture more or less will 

 occasion a variation of elasticity in the same direction of about 10 

 millimeters, (or 2 per cent.). His tests were made on first quality 

 yellow French and green Japanese silks. 



The presence or absence of gluten {gres) in silk has an appreciable effect 

 on its tenacity and ductility. In the above table the loss of tenacity 

 between l^o. 1 and Ko. 4 is 22.7 per cent., and of ductility 25.3 per cent. 

 But in other tests these figures have reached 30 per cent, for the ten- 

 acity and 45 per cent, for the ductility. 



In the matter of the charge of silk thread, it may be said that those 

 substances which coat the fibrine, such as albumen and gelatine and 

 its own gluten, probably increase the tenacity, while of those which 

 penetrate aud dilate the fibrine, some coloring matters are without 

 effect, and others, such as the metallic salts, used to excess in produc- 

 ing black dyes, reduce the tenacity materially, and often entirely, so as 

 to cause the tissue woven of it to crack when folded. 



Aside from these extraneous influences upon the elasticity and ten- 

 acity of silk, there are others inherent in the silk itself, such as the 

 volume of the thread aud the number of filaments of which it is com- 

 posed. 



The tenacity of silks is uot proportional to tlieir size. The tenacity of silks com- 

 posed of the same number of threads augments withtheir volume but by decreasing dif- 

 ferences; in other words, all conditions being equal, the liner silk is proportionately 

 stronger and its tenacity greater. 



The tenacity of silks composed of increasing numbers of filaments increases in a 

 proportion more rapid than the increase in the volume of the silks; in other -^ords, 

 the tenacity augments by increasing ditferences in a series of silks composed of in- 

 creasing numbers of filaments. 



For a given size the strongest silk is that into the composition of which enter the 

 greater number of filaments. In other words, if two silks have the same size, while 

 one is composed of four filameuts and the other of five, It is the last which is the stronger 

 aud has the greater tenacity. The tenacity in composite silks increases proportion- 

 ately with the number of contacts between the filaments. 



The mean tenacity of silk for a thread of one square millimeter cross-section is 

 43.620 K. (95 pounds). * 



*For demonstration see Maillot '^ Legons,^' etc., page 204. 

 21125— No. 10 2 



