ULTRAMICROSCOPES 
119 I 
section / pressing gently upon the quartz cover, and a top sec¬ 
tion t screwing down upon the section /. When much work is 
to be done with this device it is best to have all the screw threads 
but three turns cut from the bed-piece and a slight recess cut 
as shown at i. This permits a rapid removal of t, and / is easily 
lifted out. As furnished by the makers / is flush with the threads 
of the bed-piece b and being smooth with no milling is hard to 
remove. A small pin in / fitting into a hole in b, not shown in 
the diagram, prevents / from turning when t is being screwed 
down. 
It is absolutely essential that both cell and cover be absolutely 
clean and free from all dust particles. Unless so clean that 
when the cover is laid upon the cell and very gently pressed 
Newton’s rings can be seen the device is unfit for use. To pre¬ 
pare Q for use wash very thoroughly both pieces, immerse in 
hot chromic-sulphuric cleaning mixture, rinse with distilled 
water, follow by purified alcohol, and dry in a current of warm 
air, next support upon a loop of platinum wire and heat to a 
bright red in a Bunsen burner. As soon as the pieces are cool, 
lay in place in B, and use them at once. Wlien employing the 
quartz cell and cardioid condenser, never use anything but 
water as immersion fluid between condenser and cell. 
Use only sufficient liquid to form a thin layer q and not quite 
fill the groove o. 
The objective must be centered by means of the adapter A 
(Fig. 57), so that the bright spot of light formed in Q will fall 
in the center of the field.^ 
Always raise or lower the cardioid condenser so as to ascertain 
the proper position for the blackest background and brighest 
diffraction images. 
See that the beam of light from the radiant falling upon the 
mirror of the microscope is of sufficient diameter to fill the aper¬ 
ture of the condenser. 
Use an arc of not less than 15 amperes. 
^ For use with the cardioid ultramicroscope Zeiss supplies a special Glycerine 
immersion objective, 3 mm., N.A. 0.85 which has been corrected for quartz of the 
thickness of the cell cover. 
