1896 Journal of Applied Microscopy 



then be acidified with nitric acid, evaporated to dryness, taken up with water 

 acidified with nitric acid, and tested for lead with potassium iodide. Lead 

 sulphate is also quite soluble in solutions of many other ammonium salts, a 

 property it is well to bear in mind when engaged upon the analysis of complicated 

 mixtures. 



A convenient and simple method for ascertaining whether or not a white 

 precipitate thrown down by sulphuric acid contains lead, is to draw off the mother 

 liquor, then add to the sulphate residue a small drop of water and finally a crystal 

 fragment of potassium iodide, after a few seconds the preparation is examined 

 for the characteristic plates of lead iodide (Fig. 82). 



Exercises for Practice. 



Test a preparation of Pb(N03)2 with dilute Ho SO 4. 



Recrystallize a preparation of PbSO^ by heating it with concentrated H2SO4. 



Recrystallize another preparation by heating with strong HCl. Repeat the 

 last experiment, substituting strong HNO3 for the HCl. 



Make a mixture of Pb and Ba, precipitate with HjSO^ ; then separate the 

 PbS04 by heating with HCl. Then try a mixture of Sr and Pb. 



Try the method of separating Pb from Ba by means of NaOH. 

 Cornell University. E. M. Chamot. 



LABORATORY OUTLINES. 



For the Elementary Study of Plant Structures and Functions from 

 the Standpoint of Evolution. 



Xn. Closteritim Sp. Class, Conjugatae. Order, Desmidiales. Family, 

 Desmidiaceae. 



Desmids are quite common in ponds and lakes and species of Closterium 

 can usually be found in the sediments at the bottom, on submerged water plants, 

 or in large masses floating on the surface. Sometimes Closterium is very abun- 

 dant in watering tanks, forming large, green, floating flakes. 



1. Mount in water and observe the large bright green, unicellular plants 

 which are more or less curved or crescent-shaped. 



2. Draw an individual under high power, showing the cell wall with trans- 

 verse striations in the central region, the two large chromatophores (chloroplasts) 

 with highly refractive bodies (pyrenoids), the large nucleus with nucleolus in the 

 central, clear space, and the peculiar vacuoles at each end. Notice the dancing, 

 crystalline granules of calcium sulfate in the vacuoles (Brownian movement). 

 Describe in detail, noting especially the symmetrical halves of the cell. 



3. Notice the streaming of the cytoplasm between the large chloroplast and 

 the cell wall. Trace the current around the end of the cell. 



4. Look for dividing specimens. Draw and describe. 



5. Search for conjugating individuals and for zygospores. 



