208 
ELEMENTARY CHEMICAL MICROSCOPY 
millimeter deep, its capacity when closed with a cover-glass is 
I cubic centimeter. Counts of particles are made in as large 
a number of fields as possible, using a net eyepiece micrometer 
or an eyepiece with a central diaphragm opening adjusted to any 
convenient area on the slide. Results may be expressed either 
in numbers per cubic centimeter or in per cent by the plotting 
method described above.^ 
In the biological examination of water the microscopic organ¬ 
isms are concentrated into a few cubic centimeters of water by a 
small sand filter contained in the stem of a funnel of special 
design. The sand, together with the supernatant small volume 
of water, is emptied into a test tube, given a rotary motion and 
as soon as the heavy sand subsides, the water containing the 
organisms in suspension is poured off and one cubic centimeter 
transfered to the counting cell.^ Although used primarily for 
the purpose stated, this counting cell and method can be applied 
to many problems involving chemical analyses. 
In order to facilitate the counting and recording of the sus¬ 
pended matter found in water, Whipple has devised an eye¬ 
piece micrometer with special ruling. This type of micrometer 
has been found desirable as an aid in recording the size and 
number of masses of amorphous matter in water. By common 
consent American analysts have agreed to express these values 
in terms of the areas covered by the masses found in the cell. 
The unit employed is a square, 20 microns on a side, and there¬ 
fore equal to 400 square microns; this is known as a “ standard 
' For further applications of Method I, see Meyer, Zeit. Nahr. u. Genuss., 17 
(1909) 497: Ezendam, Zeit. Nahr. u. Genuss., 18 (1909) 462. Analysis of Starch 
Mixtures. 
Young, Bull, no. Bureau Chem., U. S. Dept. Agric.; Pollen in Honey. 
Boedemann, Landw. Vers. Sta., 76 , 134; Smut Spores in Flour, etc. 
Oerum, Biochem. Zeit., 36 (1912), 18; Fat in Milk: Vauflart, Ann. Falsif., 4 
(1911) 381; Analysis of Meals. 
Keenan and Lyons: The Microscopical Examination of Flour; Bull. 839, U. S. 
Dept Agr. Bur. Ch. 
McDonnell, Roark and Keenan: Insect Powder; Bull. 824, U. S. Dept. Agric. 
Bur. Ch. 
^ For details and precautions in water examination, the student should consult 
Whipple, The Microscopy of Drinking Water. New York, Wiley & Sons, Inc. 
