94 PHOTOMICROGRAPHY 



300 c.c. capacity are supplied, to hold suitable solutions 

 for light filters, and to act as condensers. 



To start the lamp the positive and negative supply 

 wires are joined to the proper terminals of the tube, and 

 the latter is slowly tilted to cause the mercury to flow 

 from one end to the other and back again, repeating the 

 movement if the lamp does not begin to glow. 



The following are the lines of the mercury vapour 

 spectrum : 



Yellow wave length 5790 A.U. 



5760 



Green 5460 



Blue 4360 



Violet 4070 



4050 



There are no red lines, and one of the advantages of the 

 mercury vapour lamp is the very small amount of heat it 

 gives. 



Suitable solutions to act as light filters can be made as 

 follows : 



1. To transmit yellow light X =5790 and 5760 A.U. 

 Potassium bichromate . . .15 gram. 

 Copper sulphate . . . . 3-5 ,, 

 Sulphuric acid . ; ... . 1 c.c. 

 Distilled water . . , . . 300 c.c. 



2. To transmit green light A =5460 A.U. 



Picric acid . .'., . . . 0-4 gram. 



Copper sulphate . , . . 3-5 ,, 



Didymium nitrate . . 15 ,, 



Distilled water . , ... 300 c.c. 



If the Didymium nitrate is omitted from this filter, 

 yellow-green light is passed of wave lengths 5790, 5760, 

 and 5460. 





