" Multiple Evaporation." 



an exaftly similar manner, gives off a destru6live, vicious, 

 corrosive gas. 



Having so far dwelt on the benefits to be derived from 

 a more comprehensive knowledge and data of evaporators 

 we will proceed with the points raised by Mr. LuBBOCK 

 in 1883, and Mr. SCARD in his paper before this Society. 



That there is not an equal division of temperature 

 between the units of a multiple evaporator we all recog- 

 nise, but so far cannot give a satisfa6lory explanation of 

 the why or wherefore. 



Has not the diathermancy of the various vapours, that 

 is, their transparency to heat, much to do with the work 

 of evaporators, and the unequal distribution and require- 

 ments of heat that we observe in the a6lual working of 

 multiple evaporators dealing with cane juice? 



Although the adiathermancy of substances is well- 

 known to you, perhaps it will not be out of place to give 

 a striking instance of it experienced by the writer. At 

 " Joppa," in the gardens of the late Mr. Jenner, there 

 is a glass summer house that admits the full light of the 

 sun; but its heat is prevented from penetrating by the 

 adiathermanous character of water with which the glass 

 is covered, this [)roduces a phenomenal and curious cool- 

 ness to persons inside, although exposed to the full glare 

 of the sun. 



Melloni has shown clearly that water is adiather- 

 manous, and this explains Mr. Cornish's observation 

 that the calandria water from one vessel does not deliver 

 up all the heat in passing through the next below. Hence 

 the doubtful practical economy of passing the corrosive 

 calandria water from one vessel through the next below. 



Again, from Melloni'S experiments we know that 



