640 Proceedings of the Royal Irish Academy. 
represents the amount of heat lost when one gram of hydrogen com- 
bines with 19 grams of fluorine.^ 
"We thus find 
20(o'= 19(1 + 19a)i). (4y 
1.19^4%'-^^. (5)' 
19 'nr 
Eliminating wi we obtain 
20 
.'[341o.-+38.'-361}+?I^^^^0. (6)' 
Hence we find 
, / + 0-9746966 + &c. 
"^y^P^^^^^K- 1.0861335 + &C. 
Eeasoning similar to that used in the case of hydrochloric acid 
shows that 
W'2> 1. 
We must therefore, as before, choose a negative rotation exceeding 
unity and less than the asymptote. 
6. Sydrolromic Acid (HBr). — The molecular volumes of bromine 
and hydrobromic acid are the same as those of hydrogen, chlorine, and 
hydrochloric acid. 
Mol, Vol. Bromine = = 29-304. 
5-46 
Equations (4)' and (5)' become, when y8 = 80, 
81a)' = 80 (1 + 80wi). (4)' 
l,80<-«-i.'^=ill^^. (5)' 
^80 ^ ' 
Eliminating wi we find 
81 
3{6319«.- + 160o.'-6400).l^i^^#^ = 0. (6)' 
Hence we find 
/ + 0-99380828 + &c. 
1-01912873 + &C. 
Eut, as before, w'^ > 1. 
Therefore we must choose the nea^ative rotation. 
^ Berthelot and Moissan. 
2 Because 1 gram of hydrogen and 80 grams of bromine, assumed to be 
gaseous, in uniting, give off 12100 units of heat (Thomsen). 
