FIBRES. 



281 



X.210_ 



its streugtli. Cotton is readily distinguished from FJax by 

 reference to the comparative thickness of their cell-walls, 

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

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

 atmospljere 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 cuti- 

 cula ; (3) Fineness and softness — 3*9 

 that from O. harhadense being the best; (4) Purity and 

 homogeneity, and the color. 



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

 (JBombax) belonging to the Mallow family (JMalvacem). 

 B. hepatophylhtm, 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, oft€n mixed with cotton. It is 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. Cotton fibres. 



