FIBRES. 



281 



its strength. Cotton is readily distinguished from Flax by- 

 reference to the comparative thickness of their cell-walls, 

 the presence of a euticula, and by the form of the cell. 

 When air-dry, it contaiDS 6.6 per cent, of water; in an 

 atmosphere saturated with moisture, it contains 20.9 per 

 cent, of water. The ash constitu- 

 ents amount to 1.8 per cent. For 

 determining the quality, the import- 

 ant properties are : (1) Length — long 

 staple is one inch, middle staple and 

 short staple, less than one inch ; (2) 

 Silkiness — which depends on the 

 minimum development of the euti- 

 cula; (3) Fineness and softness — 

 that from G. barbadense being the best; (4) Purity and 

 homogeneity, and the color. 



259. The Silk-Cotton is from the seeds of several trees 

 (Bombax) belonging to the Mallow family {Malvacece). 

 B. hepatopliyllum, of South America and the West Indies, 

 furnishes the largest and straightest hairs. They have a 

 lustrous appearance like silk, but are not very strong nor 

 durable. The silk-cotton is seldom used alone in spinning; 

 it is, however, often mixed with cotton. It \i seldom pure 

 white ; it verges into yellowish or brownish. The hairs are 

 generally unicellular, but occasionally two-celled ; the 

 length varies from .39 to 1.18 inches. The greatest diam- 

 eter is .00075-00016 ; mostly .00083-.00114. The thick- 

 ness of the wall is to the diameter of the cell as one to 

 ten ; cotton has relatively four times as thick a wall. The 

 cuticle is evident under the microscope. The commonest 

 use of silk-cotton is in stuffing cushions, etc. 



Fig. 349. CoUon fibres. 



