434' Mr. E. L. Garbett's Description of some Parhelia 



to illustrate, and is indeed almost self-evident), that when, in 

 the course of any chemical reaction, the constituents of a com- 

 pound are separated from one another, there is a quantity of 

 heat thereby absorbed, equal to that which would have been 

 evolved if tlie same substances had entered into combination. 

 Anplvinfr the numerical quantities, we have — 



Zn + 6 5366 



Cu + O .2394 



(Zn + 0)-(Cu + 0) 2972 



Substitution of ZnO for CuO in salts of latter 353 



3325 

 This number 3325 should, therefore, represent the heat due to 

 the substitution of metallic zinc for copper. The result actu- 

 ally obtained by direct experiment was 3435, an excellent 

 approximation when all the varying circumstances of the par- 

 ticular experiments are taken into consideration. 



On the other hand, in the combination of chlorine with zinc 



and copper, we have — 



Compound dry. Compound in solution. 

 Zn + Cl . . 6309 7025 



Zn + Cu . . 3805 4167 



2504 2858 



Neither of these numbers agrees with that first given for 

 the heat produced by the substitution of zinc for copper. The 

 thermal effects are therefore not favourable to the hypothesis 

 that the metallic chlorides exist, as such, in solution. 



In makinfT these observations, I do not wish to attach to 

 them more importance than they deserve. I am fully aware 

 of the uncertainty of conclusions derived from a new and dif- 

 ficult inquiry. But as the heat developed in chemical reac- 

 tions may be taken as a measure of the forces brought into 

 play, I deemed it proper to refer to the foregoing cases, if only 

 for the purpose of directing attention to the intimate relations 

 which inquiries of this kind have with some of the most inter- 

 esting questions of molecular chemistry. 



LX. Description of some Parhelia seen at Portsea on the 

 29th of March 1848 ; "with some Remarks on these Phcenomena 

 generally. By Edward Lacy Garbett*. 

 [With a Plate.] 

 I. Description, 



THE accompanying drawings represent two exhibitions of 

 parhelia which were seen at Buckland, a village about the 

 centre of the isle of Portsea, on the 29th of March last. 

 • Communicated by Professor Miller of King's College, London. 



