CHEMICAL MICROSCOPY 



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Low temperatures of —100, — 120°C are obtained by circulating 

 in the cold stage a cooled gas such as dry nitrogen, which is cooled 

 in a coil immersed in liquid nitrogen (A. H. Thomas, W. C. McCrone). 

 In most cold stages, carbonic acid snow is used as it readily provides 

 temperatures down to — 60°C approx. (Reichert, Leitz). 



Fig. 1 1.2. Reichert hot stage microscope. 



Inserting a hot stage or a cold stage between the condenser and 

 the microscope objective brings about a gap between these two elements 

 thus frequently precluding the use of a hot or cold stage in conjunction 

 with a phase-contrast or interference microscope. The condenser 

 diaphragm to be imaged on the phase plate in the objective is not 

 always in the focus of the condenser thus preventing coincidence of 

 the diaphragm image with the phase plate. Some hot stage microscopes 

 were designed for phase-contrast and dark-ground applications and 

 also, providing reflected-light observation by means of a vertical 

 illuminator (Reichert). Figure 11.3 shows the O. P. L. microscope, 

 fitted with a hot stage designed for investigating opaque objects. 



Peltier-effect apphcations to hot or cold stages have been made 

 in the U.S.S.R. Let us take two welded metals, A and B, and insert 

 these two conductors in series in a circuit through which electric 

 current is flowing. If the current travels in the direction AB, either 



