FIBER CROPS 309 



equally divided between North and South America. Manila 

 hemp comes principally from the Philippines, and sisal hemp 

 and istle from Mexico, while jute comes from India and China. 

 All other vegetable fiber plants are secondary in importance to 

 cotton, which is also gaining in importance compared with wool 

 or silk. 



Practicums 



398. IDENTIFICATION OF FIBERS. Give each student one gram each of silk, 

 wool, cotton, and two grams of a piece of cloth composed of silk, wool, and 

 cotton, all having been soaked in ether or benzine to remove possible material 

 which may prevent action of reagents. 



Place the samples of silk, wool, and cotton in small beakers and add 10 

 per cent, solution of caustic soda (NaOH). The cotton remains insoluble; 

 the silk and wool are dissolved. To the alkali solution add lead acetate. In 

 the case of the silk the solution does not blacken, 1 but in the case of the wool 

 it does on account of the formation of lead sulphid. Pick apart the piece of 

 cloth so that the reagents may act readily, place in beaker and add a solu- 

 tion of basic zinc chlorid, made by taking a solution of zinc chlorid of 1.70 

 specific gravity, and dissolving it in an excess of zinc oxid. Heat for five 

 minutes and filter. The silk having been dissolved the loss is the silk originally 

 present. Heat the residue in 10 per cent, solution of caustic soda, and filter. 

 The loss represents the wool originally present; the residue is cotton. 1 



To determine the amounts quantitatively it will be necessary to determine 

 the percentage of moisture present, and also the finishing materials and col- 

 oring matters which may be present. These may be removed by boiling in 

 a 1 per cent, solution of hydrochloric acid, then in a 1/20 per cent, solution 

 of sodium carbonate, and finally in water. 



399. MICROSCOPIC EXAMINATION OF FIBERS. Give each student a small 

 sample of wool, silk, cotton, flax, and manila hemp, and also a piece of cloth 

 composed of wool, silk, and cotton. Prepared slides showing cross sections 

 and longitudinal view of fibers are also desirable. A compound microscope 

 with one-sixth inch objective is required, and a camera lucida is desirable, 

 but not necessary. Answers should, as far as possible, be illustrated with 

 sketches. 



Surface of fiber: smooth; scaly; sketch. 



Frequency of twist or scales: give number per definite length or area 



Luster by reflected light: high; medium; dull. 

 Transmitted light: transparent; translucent; opaque. 

 Ends of fiber: forked; pointed: sharp; blunt. 

 Length of fiber : ; breadth 



!For further details, see U. S. Dept. Agr., Fiber Investigations Rpt. No. 

 9 (1897), p. 354; also Matthews: Textile Fibres, p. 247. 



