398 BIOT ON THE EMPLOYMENT OF POLARIZED LIGAT 
If we take into consideration the progressive change of the 
colour of the liquid, we see, by the numbers of this table, that 
the rotatory power of the active substance remained sensibly 
constant from the first instant of liquefaction until Thursday 11, 
when the molecular disaggregation of the starch was sufficiently 
complete for the precipitation in water no longer to take place. 
But the progressive weakening of the rotatory power, commen- 
cing at this point, shows that the acid had begun to alter gradu- 
ally the constituent molecules of the starch, and to change it 
into another product of smaller, or perhaps inverse rotatory 
power. To follow further this reaction, and to determine its 
final product, it would be necessary to make the experiment on 
masses whose elements were determined by weight, and to exa- 
mine the properties, both chemical and physical, of the result of 
the transformation; but this research can only be successfully 
undertaken with the aid of chemical knowledge, which I should 
not have been able to bring to it. 
