55 
“The tenacity of silk thread is well known; a thread of raw silk of 
10 deniers easily supports a weight of 50 grams* without breaking. 
Direct relations exist between the tenacity of silk, the country in which 
it originates, its hygrometric state, the processes by which it was reeled, 
etc. Relations not less interesting may be found between the elasticity 
and the ductility.” t 
In the silk which constitutes the cocoon as made by the worm we find 
three classes of material. They consist of a waxy substance soluble in 
boiling water, of a gluten soluble in certain acids and alkalies, and es- 
pecially in a solution of soap, and of the fibrine which constitutes the 
base of the thread. In the yellow silks there is also a slight quantity 
of coloring matter. Robinet found from 4 to 5 per cent. of the waxy 
substance, which, being soluble in boiling water, disappears in the proc- 
ess of reeling. We therefore find in reeled silk the gluten, or, as it is 
technically called, grés, and the fibrine. Before this silk can be prop- 
erly dyed it is essential that a certain portion of this gluten be re- 
moved. This operation is usually performed by boiling it in a solution 
of soap. At the Conditioning Works at Lyons, France, this boiling off, 
as it is called, consists of two operations. The silk is first submitted 
for thirty minutes to ebullition in a solution containing an amount of 
soap equal in weight to about 25 per cent. of the weight of the silk 
boiled off. This silk is then wrung, in order to free it from the soap and 
the dissolved gluten, and then resubmitted to the same operation of 
boiling. Asa result of these tests, it is found that white French silks 
contain 19.68 per cent. of gluten and the yellow silks 22.84 per cent. 
Silks coming from Italian filatures contain an amount of gluten slightly 
in excess of these figures, while the Chinese silks exceed them by more 
than 2 per cent. 
The silk thread is highly hygrometric, containing under ordinary con- 
ditions 10 to 12 per cent. of water, while a thread of raw silk is capa- 
ble of absorbing 21 to 26 per cent. Humidity augments the ductility 
of silk and slightly diminishes its tenacity. 
* 100,000 times the weight of a piece 50 centimeters long. 
t Adrien Perret, ‘Monographie de la Condition des Soies de Lyon.” 
