452 ELEMENTARY CHEMICAL MICROSCOPY 



whether the material meets the specifications as to size of grains and per cent of 

 fine and coarse grains. 



II. QUANTITATIVE ANALYSIS. (See pages 200-205.) 



Examine mixtures of known percentage composition. Plot the curve for the 

 results obtained. Procure from the instructor a sample of unknown percentage 

 composition. Treat it exactly as the known mixtures were treated. From the 

 counts obtained determine the percentage composition by means of the curve 

 plotted. 



III. THE POLARIZING MICROSCOPE. (See pages 54-57.) 



Center the stage. Test for crossed nicols and ascertain the zero point of the 

 analyzer. Test the accuracy of the cross-hairs, the graduations on the circumfer- 

 ence of the stage and those on the analyzer. (Use ammonium sulphate.) 



Examine, sketch and describe the appearance of the salts listed on the bulletin 

 board. Follow the suggestions given on page 269. Try all the experiments listed 

 on the bulletin board. Having completed the work outlined, apply to the instructor 

 and obtain a series of salts. Determine their extinction and their probable crystal 

 systems. Measure the plane angles and the extinction angles of the salt indicated. 



IV. REFRACTIVE INDEX. (See pages 226-243-) 



1. Perform the experiments with air bubbles and ivith oil globules as described on 

 pages 229-230. Then study the phenomena exhibited by glass rods and glass tubes 

 of almost microscopic diameters when illuminated and focused in the same manner 

 as employed on the air bubbles and oil globules. Examine the rods and tubes in 

 air, in water and in oil; note well the changes in the character of the contour bands. 



2. By the immersion method measure the refractive index of (a) KC1; (b) KBr. 

 (See pages 227-234.) Obtain from the instructor an " unknown " salt; deter- 

 mine its refractive index. 



3. Calibrate the brass cell numbered the same as your microscope. (See page 

 241.) Plot the curve for the cell on an 8 X 10 sheet of coordinate paper. Obtain 

 from the instructor a liquid of unknown refractive index; determine its refractive 

 index, using the calibrated cell. 



V. COMMON TEXTILE FIBERS. 



Place a little of the material in a drop of water upon an object slide. After 

 soaking for a few minutes, tease apart with dissecting needles so as to obtain from 

 the bundles of fibers a few of the ultimate component fibers or cells. Cover with 

 a cover-glass and study these component fibers. Raise and lower the substage 

 condenser with open and closed diaphragm. Test the effect of oblique trans- 

 mitted light. Examine between crossed-nicols in order to ascertain intensity of 

 polarization and to render striations, cross-hatchings and nodes more easily dis- 

 cerned. Make diagrammatic sketches of the different fibers studied and note the 

 characteristic features observed with each fiber. Defer testing with stains and 

 reagents until paper fibers are taken up. 



