HEAT OF FORMATION 93 



1 S $ O F Cl Br I 



i 6 3-0 26-7 29-4 22-7 138 



only that the heat of combination of fluorine is out of 

 place, because it refers to the dissolved salt, for which the 

 numbers for the chloride bromide and iodide would be 

 13-6, 2-4, and 13-1. 



It is quite otherwise with the elements that are commonly 

 known as non-metals. We will arrange the data for these 

 in a table alongside of those for sodium by way of com- 

 parison ; the numbers are again for formation of the product 

 in aqueous solution, so far as that exists. 



Na H P C S Ni O Cl 



It is to be noted that : 



For hydrogen the values stand in the same order as for 

 sodium, except that the difference of thermal effect due to 

 combination with oxygen and chlorine is reduced, and would 

 even be reversed if the heat of solution of hydrochloric 

 acid (17) were not taken into account, in which case the 

 value for chlorine would be only 39 17 = 22. 



For phosphorus the value for combination with oxygen 

 is actually the greater, and for sulphur the excess reaches 

 a maximum. 



Going further to the right, a second characteristic appears, 

 since the heat of combination with hydrogen increases, 

 becoming equal to that for combination with chlorine, in 

 the case of carbon and sulphur, and exceeding it for nitro- 

 gen, oxygen, and chlorine ; so that at the extreme right, 

 for chlorine the relative magnitude of the quantities of 

 heat is reversed in almost every respect : this is shown by 



1 Refers to formation of the silver compound (Ag a C a ) = 87-15, 

 Centralblatt, 1899, n. 583. 



