2 5 8 



PRACTICAL MICROSCOPY. 



number recorded on the scale, but is only to be used for 

 measuring between lines, and for this purpose it may be 

 trusted. 



Dr. Lawson has suggested that the great advantage of 

 this contrivance is that it does not monopolise one of the 

 two spectra, as with the use of the quartz scale; for in 

 describing two spectra, only slightly differing from each 

 other, it may be used at once to determine the difference 

 between them. 



In concluding this chapter it may be as well to give a 

 short list of substances showing well-defined absorption 

 bands, such as may be of use to the student upon commenc- 

 ing to use the instrument. 



Nitrate of didymium. 

 Oxalate of ,, 



Oxide of (blowpipe- 



bead). 

 Chloride of cobalt (in alcohol). 



(in chloride of 



calcium). 



(a crystal). 



Cobalt glass (blue). 

 Sulphate of uranium. 

 Acetate of .. 



Oxalate of chromium and soda. 



Sulphate of chromium. 



Permanganate of potash. 



Ruby glass (copper). 



Ammonio-sulphate of copper. 



The aniline colours. 



The naphthalene colours. 



Indigo sulphate. 



Carmine. 



Litmus (blue and red). 



The colouring matters of plant petals. 



