QUANTITATIVE ANALYSIS BY MEANS OF THE MICROSCOPE 215 



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 one 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 1 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 

 size by the number of fragments and the specific gravity of 

 the fiber. 



Quantitative microchemical methods with reference to the 

 handling of minute amounts of material and weighing on a 

 Nernst micro balance; the titration of tiny volumes of liquid; 

 the measurement of tiny volumes of gas, etc., which do not re- 

 quire the application of the microscope need no discussion here, 



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



