QUANTITATIVE ANALYSIS BY MEANS OF THE MICROSCOPE 211 



may be made it is essential that the globules of metallic mercury 

 shall never be so large that they become flattened and thus not 

 perfect spheres. In determining the diameter of the spheres 

 proceed exactly as described above, always making several 

 measurements of the sphere diameters. From the average of 

 the data thus obtained, calculate the weight W = (d 3 X 0.5236) 



X 13.59. 



In estimating the percentage of the different fibers entering 

 into the composition of a given sample of paper, it is customary 

 in most commercial paper- testing laboratories to guess at the 

 per cent of a given fiber without comparison with standards and 

 without counting the fibers, the usual practice being for several 

 analysts to " guess " at the composition independently. These 

 men in time become very expert and their findings will generally 

 check within i per cent. In the opinion of the author, com- 

 paring with known standards, using the comparison microscope 

 or comparison eyepiece is quicker and gives a more reliable 

 approximation. 



Herzog * has suggested a microscopic method for the quan- 

 titative estimation of the different fibers in fabrics, or for the 

 per cent of different colored fibers in a fabric. Stated briefly, 

 the process is as follows: A tiny piece of the fabric is imbedded 

 in paraffin (M.P. 60) by repeated dipping. After cooling, 

 sections about o.i to 0.2 millimeter are cut by means of a razor 

 or microtome knife. One of the sections is transferred to an 

 object slide, warmed until the paraffin melts and is tipped back 

 and forth to evenly distribute the fiber fragments. A drop 

 of balsam is placed upon a cover glass and lowered upon the 

 preparation. The entire number of each different fiber is then 

 ascertained by counting, using a net eyepiece micrometer. 

 Having thus found the relative proportion of the fibers, their 

 absolute size is next determined by measurements of length 

 and thickness, or since the thickness of the section cut is 

 known and the average diameter of different fibers is also well 

 established, actual dimensional measurements may not be re- 

 quired. The weight is calculated by multiplying the absolute 



1 Herzog, Z. Chem. Ind. Kol., I (1907), 202. Z. Text. Ind., 1906, No. 4. 



