14 
IOWA ACADEMY OF SCIENCES. 
inversely proportional to the molecular weight of the substance 
dissolved; second, the elevation of the boiling point of a solvent 
is directly proportional to the amount, and inversely propor- 
tional to the molecular weight of the substance dissolved. An 
important apparent exception to these laws which will be con- 
sidered later, was found in the case of those substances which 
are good conductors of the electric current, that is, of electro- 
lytes. The laws were further found to be limited in their 
application to dilute solutions. 
Important as this principle was in furnishing a method for 
the determination of molecular weight of those compounds, such 
as the sugars, which can not be converted into vapor, its purely 
empirical character, and the important apparent exception 
above stated, prevented for a time its receiving the considera- 
tion and acknowledgement which were intrinsically due to it. 
It could not meet general acceptance, or be received with 
confidence until deprived of its empirical character by a general _ 
theory connecting the phenomena in question with other known 
facts, and until its seeming exceptions met a satisfactory 
explanation. 
In due time Van’t Hoff enunciated the theory and Arrhenius 
furnished the explanation. 
Raoult’s first law may be expressed by the equation 
m = K I a 
' V ' t: 
in which m = the molecular weight of the substance dissolved, 
a = the specific depression, that is the lowering of the freezing 
temperature due to dissolving one gram of substance in one hun- 
dred grams of solvent. K = a constant dependent upon the 
nature of the solvent only. 
Raoult’s second law may be expressed by the following sim- 
ilar equation : 
m = k I 
in which E is the sj^ecific elevation, or elevation of boiling tem- 
perature due to dissolving one gram of substance in one hun- 
dred grams of solvent. 
Now, Van’t Hoff, by means of an imaginary cycle of opera- 
tions, conceived in analogy with Carnot’s famous cycle to which 
the science of thermodynamics owes so much, showed that the 
constant, K; of Raoult’s formula must be a function of the tem- 
perature and of the heat of fusion of the solvent, of the form 
