CH. XIV] LIGHT AND ENERGY LOSSES IN PROJECTION 607 



850. Table of the energy and light transmission and 

 absorption. 



851 . Other substances dissolved in water. Other substances 

 dissolved in water have not been found to improve its energy 

 absorbing qualities. For a long time it was supposed that a 

 saturated solution of alum was more effective than pure water but 

 this is not so; moreover it is very difficult to prepare a saturated 

 solution of alum which is not turbid. Tests show energy trans- 

 mission of 22.8% for an alum solution as against 22.9% for clear 

 water, while alum absorbs 15% of light as against only 10% for 

 clear water. The alum only serves to dilute the water. Crystals 

 of alum, K 2 SO4 A1 2 (S0 4 )3 24 HgO, absorb much energy, but it has 

 been proved that this is entirely due to the water of crystallization. 



852. Energy losses in the specimen. All the light energy 

 absorbed by the specimen is converted into heat ; hence, an opaque 

 specimen or one which is black would become heated in the con- 

 centrated beam of light necessary for the microscope even if only 

 the radiation in the visible spectrum were used. As the visible 



