158 
ELEMENTARY CHEMICAL MICROSCOPY 
pressed air and be furnished with binding posts or switch for 
electric current (direct, when available). Running water is 
unnecessary. 
The arrangement of instruments, apparatus and reagents 
upon the work table is shown in the cut and needs no further 
comment. 
A stool adjustable in height and provided with a swivel seat 
may be said to be practically indispensable. If the stool has in 
addition an adjustable back the added comfort thus secured 
cannot be overestimated. 
Radiants for Microscopic Illumination. — The modern micro¬ 
chemical laboratory employs as sources of artificial light for 
microscopic illumination the electric current or the acetylene 
light. Gas-light illumination, using Welsbach mantels, made 
incandescent by coal gas, alcohol or gasoline vapors, have already 
become radiants of the past, and the oil lamp is now so very 
rarely used as to need no comment. If Welsbach lights must 
be employed owing to lack of electric current or calcium carbide, 
preference should be given to lamps of the inverted mantle 
type. 
Cylinders containing compressed acetylene gas are now so 
widely distributed and the gas relatively so inexpensive (exclud¬ 
ing the first cost of the container) that few investigators will care 
to be bothered with carbide gas generators. A piece of thin 
faintly blue glass placed between the acetylene flame and the 
mirror of the microscope yields light approximately equivalent 
to daylight, so far as color values are concerned.^ 
The development of dark-ground and of vertical illuminators 
and their applications has been accompanied by a corresponding 
improvement in electric lamps. These now fall in one of several 
groups; carbon arc lamps, Nernst glower lamps, tungsten fila¬ 
ment incandescent lamps or mercury vapor lamps. 
Ordinary microscopic work rarely requires an arc lamp draw- 
1 Wright, Artificial Daylight, Amer. J. Sci. (4) 27 (1909), 98. Quite recently 
the Corning Glass Works of Corning, N. Y., has perfected a blue glass such that, 
when employed with large tungsten lamps, true artificial daylight is obtainable 
as shown by spectroscopic tests. 
