METHODS OF INVESTIGATION 7 



The loss in weight is chiefly due to the removal of 

 casual impurities. 



Determination of the Length and Diameter of Ultimate 

 Fibres. A portion of the cellulose, obtained in 

 the manner described above, is placed in dilute 

 acetic acid, teased out with needles, and mounted on 

 a glass slip. The length and diameter of a number of 

 fibres thus separated are determined by means of 

 the microscope, and the maximum, minimum, and 

 average measurements are recorded. These con- 

 stitute very important factors in the valuation of 

 fibres, and are of assistance in determining their 

 suitability for different manufacturing purposes. 



Determination of Strength and Elongation. The strength 

 of fibres may be determined roughly by hand, but 

 considerable practice is required before it is possible 

 to form an accurate judgment in this way. 



To obtain more definite and strictly comparable 

 results, recourse should be had to one of the machines 

 which have been specially designed for this purpose. 

 In order to obtain trustworthy figures, it is necessary 

 that a large number of determinations should be 

 made, and the average calculated. 



Among the machines which have been devised for 

 the measurement of strength and elongation under 

 stress (sometimes inaccurately termed elasticity), 

 reference may be made to that of Schopper of Leipzig 

 and that of Reeser and Mackenzie of Philadelphia. 



In Schopper 's machine, the fibre is clamped in a 

 vertical position between two jaws, the upper of which 

 is attached to one end of a horizontal beam, whilst 

 the lower is connected to a piston which moves in 

 a cylinder, and is lowered or raised by means of 

 hydraulic pressure. A pointer attached to the beam 

 is caused to move over a graduated scale as the 

 tension on the fibre increases. Immediately the fibre 

 breaks, the pointer stops, and thus registers the 

 breaking-strain on the scale. By means of an in- 

 genious arrangement, the elongation undergone by 

 the fibre before breaking is also recorded. This 

 machine can be used for any of the ordinary fibres, 

 and can be employed for the coarser fibres for which 



