172 



Prof. B, Moore and Mr. T. A. Webster. 



It is accordingly of some interest to enquire whether such transforma- 

 tions of sunlight into chemical energy by inorganic transformers are 

 associated with a temporary chemical change from a higher to a lower oxide, 

 or whether the change is a surface action in which the light-energy is con- 

 verted into chemical energy at the surface of the colloidal aggregate. 



Our experiments favour the latter view, for if the lower oxide reacted 

 with the water and carbon dioxide to form formaldehyde, then a greater 

 reactivity might be expected when ferrous salts were employed instead of 

 ferric salts ; this is, however, not the case, for we have found ferrous salts to 

 be entirely inert, nor have we been able by titration with permanganate to 

 show any formation of ferrous salts when ferric salts are exposed in aqueous 

 solutions in presence of carbonic acid. Moreover, many of the active 

 inorganic transformers which we have lately investigated, as recorded below, 

 do not form higher and lower oxides under the conditions in which we have 

 used them. It is therefore probable that the energy transformation is one 

 induced by the energy of the light at the surface of the colloid particle upon 

 which probably carbon dioxide concentrates. 



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 distinctly 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, and 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 cm. from a 

 mercury vapour arc in a quartz tube. 



B. Action of Stmlight and of Ultra-violet Light upon more Concentrated 

 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 com- 

 bustion of six gramme-molecules of formaldehyde should be almost equivalent 

 to that of one gramme-molecule of a hexose sugar. For example, the 



