QUANTITATIVE MICROSCOPIC DETERMINATIONS 169 



ments, distinctly recognizable as such are to be counted as one, and it 

 is important that all of the comparative counts be made of powders of 

 the same degree of fineness. The percentage estimates based upon 

 the counts of the first year and the second year leaves will be quite 

 variable and will show wide ranges in results. 



6. Glycyrrhiza. Prepare samples of pure average samples of the 

 peeled and the unpeeled licorice, and of licorice trimmings. Counts 

 are made of the yellowish groups of fibrous tissue, especially of the 

 groups of crystal bearing fibers. The starch count may be ignored. 

 In the case of the unpeeled licorice a count is to be made of the dark 

 brown cork tissue elements. The following counts are to be made 

 of the three samples. 



(ft) The number of cork tissue elements and groups of such ele- 

 ments in the unpeeled licorice ; also a count of the yellow fibrous tissue 

 and crystal bearing tissue groups. 



(6) The fibrous and crystal bearing groups in the peeled licorice. 



(c) The number of fibrous tissue groups in the licorice trimming. 



Make admixtures of the pure licorice and of the licorice trimmings 

 and determine the percentages of the admixtures from the results 

 of the counts. The results of the counts will again be utilized in 

 exercise ten. 



7. Sublimed Sulphur. Examine carefully samples of pure sublimed 

 and of precipitated sulphur and note the microscopic differences. 

 Make careful percentage admixtures of sublimed sulphur in plain 

 vaseline and from such admixtures make the counts of the sulphur 

 particles. A 1, 5 and a 10 per cent, mixture should be counted. If 

 it is found that the sulphur particles are too numerous to permit 

 counting then dilutions must be made and the percentages redeter- 

 mined from a carefully prepared 1.5 per cent, vaseline suspension. 

 How many particles of the sublimed sulphur in one gram? The 

 results of the counts are to be used in exercise ten. 



8. Black Pepper. Four substances are required; an average com- 

 mercial sample of pure whole black pepper; an average commercial 

 sample of whole white pepper; a sample of whole pepper known in the 

 trade as "grinding peppers;" and a sample of "black pepper refuse" 

 (consisting of pepper stems, tailings and screenings). These several 

 samples are to be reduced to the same degree of fineness and the 

 following counts made. 



(a) Of the black pepper, the dark to nearly black fragments and 

 groups, consisting entirely of the pericarp tissue; and the colorless 

 tissue fragments (starch bearing) consisting wholly of the endosperm 

 tissue elements. The counts represent 100 per cent, black pepper. 



