ENERGETICS 



45 



As will be seen in subsequent pages, this process is representative of many of those occurring 

 in living cells. I found (1906, p. 187) that the amount of dye which a piece of paper of a 

 certain size will take up from a given solution of Congo-red, if allowed to remain in it until 

 no further amount is taken up, is lesft at 50 than at 10. Now, whether this process is one 

 of pure adsorption ( = surface condensation) or also partly chemical, it is no doubt associated 

 with the production of heat. Calling the system, paper in contact with dye solution, A, 

 and the dyed paper, B, van't HofFs law, the first case above, tells us that rise of temperature 

 causes increase in A, as experiment shows. 



Although, however, at the higher temperature there is less product formed, yet 

 the rate at which this is formed is greater. The curves of Fig. 29 serve to show 

 this fact. It will be seen that, at the higher temperature, equilibrium was 

 attained in about 100 minutes (curve a), whereas at the lower temperature 

 (curve b), it was not quite complete at the end of the experiment (twenty-four 

 hours). The amount taken up at the lower temperature was rather more than 



90- 



80- 



70- 



60- 



20 40 60 so too 



300 



400 



500 



FIG. 29. 



EFFECT OF TEMPERATURE ON THE RATE OF ADSORPTION OF 

 CONGO-RED BY PAPER. 



Abscissae time in minutes. 



Ordinates total amount adsorbed at the time 



a, at 50. 



b, at 10. 



At the higher temperature, the rate of adsorption is faster, although the total amount adsorbed when 

 equilibrium is reached is less. , _ . 



(Bayhss, 1911, 1, p. 17.) 



one half of that originally present in the solution ; at the higher temperature, 

 only one quarter. This experiment will be found (Chapter XXI.) to have some 

 bearing on the way in which oxygen is carried by haemoglobin. 



The great influence that temperature has on both rate and equilibrium in 

 chemical and physical processes necessitates care in the maintenance of a constant 

 known temperature in investigating them. The means of doing this will be found 

 in the textbooks dealing with practical physical chemistry, such as those 

 Findlay, Ostwald-Luther or Spencer. 



SUMMARY 



The essential characteristic of life is incessant change. To produce change, 

 work must be done. The power of doing work is due to the possession ol 



Of the two great laws dealing with energy, the first tells us that, while any 

 one kind of energy may be transformed into any other kind, there i 

 gain or loss. 



