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. 1 



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. 



