132 APPENDIX 



made by the removal of Smith's Island opposite the city. In the city proper, it may be 

 stated briefly that material may be found in a stratum of very light blue clay at a depth 

 varying from twenty to sixty feet in many places south of Arch St. east of Broad St., and 

 also along the beds of ancient rivulets near Tioga St., at Sixteenth St., and in certain other 

 places which were probably subject to tidal overflow. One of the best collections was 

 made along the bank of the Schuylkill at the east end of Walnut St. Bridge, at a depth of 

 thirteen feet below the surface. Excavations for the Reading Terminal and the Subway 

 and several buildings, as the Bingham House, have furnished numerous specimens. 



Cleaning the Material. Some gatherings may be so pure as to be ready for mounting 

 when treated with dilute alcohol and oil of cloves. If, when gathered, the diatoms are 

 immersed in a saturated solution of picric acid for several days, they may be stained with 

 carmine or methylene blue, or whatever may be required to emphasize the contents of the 

 frustules, including the endochrome and the pyrenoids. After staining, pass as rapidly as 

 expedient through the treatment with dilute alcohol and oil of cloves, and mount in benzol 

 balsam, avoiding heat. A hot solution of mercuric bichloride is sometimes used for the 

 preservation of the endochrome, although washing is needed before mounting. For the 

 particular stain considered best for certain details of structure, it will be advisable to con- 

 sult works on Micro-Chemistry or Heinzerling (I. c.). The stains of most importance are 

 carmine, methylene blue, hsematoxylin, gold chloride and Bismarck brown. 



Whatever method may be used in staining, the identification of forms is impossible, 

 in most cases, unless the valves are carefully cleaned and the cell-contents destroyed. For 

 this purpose provide a casserole holding from five to eight ounces, an iron tripod stand 

 with alcohol lamp, several six-inch test-tubes, preferably those with a standard base, fitted 

 with pure rubber corks. Take the material as free from twigs, dead leaves, sand, and other 

 matter as possible, place it in the casserole, and add about the same quantity of nitric acid. 

 Boil for twenty minutes and then add about half a teaspoonf ul of powdered bichromate of 

 potash, stirring with a glass rod. Then take a beaker-glass partly filled with water and pour 

 into it slowly the liquid which has been allowed to cool a short time, whirling the casserole 

 to cause the concentration of sand in the centre. Allow the material to settle for half an 

 hour or longer, according to the amount of diatoms and their size. Pour off the water, 

 add more water, and place in a test-tube. Repeat the decantation, shaking the test-tube, 

 closed with a rubber cork, vigorously each time. From time to time whirl the diatoms in 

 the casserole and throw away the sand collected hi the centre. By repeating the decanta- 

 tion, shaking and whirling, the deposit will be found to consist almost entirely of diatoms. 

 It may be necessary to repeat the boiling in the acid and bichromate. If, however, any 

 detritus other than sand is noted, boil in sulphuric acid and add from time to time minute 

 pinches of powdered chlorate of potash, being careful to protect the eyes by holding a 

 piece of glass before them; otherwise the explosions which occur are likely to throw some 

 of the boiling acid into the eyes and destroy the sight. The material, when clean, should be 

 white or, hi the case of Synedra, yellowish. It is quite easy to construct a box fitted with 

 the proper apparatus for boiling and provided with a glass door for observation, and a 

 method of introducing the chlorate of potash through a small aperture or tube. The box 

 may be placed in the garden or fastened outside of a window so that the poisonous fumes 

 may be carried off. 



An excellent method, hi the case of larger forms, is to boil the material already cleaned 

 by the acid in water to which a few shavings of coarse brown soap are added. The differ- 

 ence in density will hold hi suspension any flocculent matter, and while many of the smaller 



