256 Cellulose 



to, the form of energy which we are bound to express by the some, 

 what colourless term ' vital force ' must exhibit a specially plastic 

 constitution. The peculiar sensitiveness of the carbohydrates as 

 a group to fermentation and other decompositions is not sufficiently 

 accounted for by the constitutional formulas assigned to them. 



Destructive Distillation. Theoretical Notes. We may by care- 

 ful consideration form some mental picture of the consequences 

 of the addition of heat to compounds of this class. As a preliminary 

 it is necessary to remember generally the distinction between the 

 purely chemical and the chemico-physical view of the constitution 

 of matter. According to the former, cellulose is a compound 

 72.C 6 Hj O 6 , of which the ultimate constituent groups CO CH 2 

 CHOH are arranged in a certain way in the C 6 units ; and these, 

 again, are grouped together in a special configuration which, when 

 elucidated, will represent the molecular constitution of cellulose. 

 The correlative of this view is that of the intrinsic or internal 

 energy of the compound. This is expressed as a crude aggregate 

 on the thermo-chemical view as what is known as the ' heat of 

 formation,' which, in the case of carbon compounds, is the difference 

 between the sum of the heats of combustion of its constituents, 

 and the heat of combustion of the compound itself, expressed in 

 arbitrary units of mass, usually the gramme, but in molecular 

 ratios. The methods of determining combustion-heats are neces- 

 sarily subject to errors of observation of some magnitude ; but, 

 even with much closer approximation to accuracy, the number of 

 calories per gram-molecule of a compound evolved on burning is 

 still of only empirical and statistical value, even when applied to 

 compounds related in differential series. 



Whatever the meaning of the constant of energy, which we regard 

 as associated with every particular configuration of matter, it is at 

 least obvious that all compounds with which we are familiar repre- 

 sent an equilibrium of matter and energy under the conditions of 

 observation ; and as combination is generally associated with loss 

 of energy, so, vice versa, the introduction of energy implies decom- 

 position or tendencies to decomposition. The communication of 

 energy in the form of the electric current, as in electrolysis, is 

 usually attended by more or less simple decompositions, more or 

 less easy, therefore, to follow. The effects of heat, on the other 

 hand, are complicated by recombinations of the products amongst 



