ON ORGANIC COMPOUNDS 83 



A number of other solutions were then tested after exposure 

 to the rays from a quartz mercury vapour arc. In addition to the 

 ferric salts and uranic salts, strong positive results were obtained 

 with 1 per cent, solutions of dialysed silicic acid, and with a 1 per 

 cent, solution of beryllium chloride; less active solutions, but dis- 

 tinctly positive in 1 per cent, solution, were copper chloride and 

 sulphate, nickel chloride, palladium chloride, manganese chloride, 

 erbium chloride. Negative results were given by ferrous sulphate 

 and chloride, sodium silicate, an undialysed hydrochloric acid 

 solution of silicic acid, zinc chloride, cobalt chloride, potassium 

 chloride and chromate, barium chloride, aluminium chloride, borax, 

 and telluric acid. 



The above-named solutions were exposed in each case for a 

 period of four to five hours in transparent quartz test-tubes, at a 

 distance of 7 cms. from a mercury vapour arc in a quartz tube. 



Action of Sunlight and of Ultra- Violet Light upon more Concen- 

 trated Solutions of Formaldehyde. When formaldehyde is once 

 formed by the action of sunlight from carbon dioxide and water, 

 practically all the energy necessary for formation of carbohydrates 

 by the condensation of formaldehyde groups has been absorbed; 

 for although the heat of combustion of formaldehyde has never 

 been determined, judging from analogy in similar cases, the heat 

 of combustion of 6-grm. molecules of formaldehyde should be 

 almost equivalent to that of 1-grm. molecule of a hexose sugar. 

 For example, the energy of formation, or combustion, of 2-grm. 

 molecules of any hexose is almost equivalent to that of 1-grm. 

 molecule of a biose or disaccharide, and all sugars and starches 

 possess almost equal stores of chemical energy in equal masses. 



As will be shown in a later chapter, it is under such conditions 

 that the typical reactions in living systems occur. When the total 

 chemical energy of the reacting substances on either side of the 

 equation is large, but the difference on the two sides is small, then 

 typical reversible reactions are seen with the equilibrium point a 

 considerable distance removed from either end-point. 



This condition of affairs so characteristic of biochemical reactions 

 is due to a labile balance between osmotic energy and chemical 

 energy, and it is for this reason that conjugation with formation of 

 more complex molecules is favoured by higher concentration, whereas 

 dilute solution favours cleavage into simpler molecules. This point 

 is of great importance in biological synthesis, and for understanding 



