6 Proceedings of the Royal Irish Academt/. 



Efects produced hy treating water Ejctracts of Leaves and some pure 

 Organic Substances ivith Oxidizing Agents. 



Some effects that we observed led us to try the action of oxidizmg agents 

 on the photo-electric activity of water extracts from leaves, and also the 

 action of oxidizing agents in the case of solutions of some pure organic 

 substances. 



As oxidizing agents we employed lead peroxide or potassium permanganate 

 solution. Lead peroxide, whether dry or suspended in water, is practically 

 inactive as regards photo-electric effect, and so also is potassium permanganate. 

 Water extracts from many types of leaves were treated with one or other of 

 these oxidizing agents, and in nearly every case we found a large increase of 

 photo-electric activity. Sometimes there was no increase from treatment 

 with lead peroxide, but there was an increase when potassium permanganate 

 was used, and in a couple of instances the increase was more marked with the 

 lead peroxide. It is not necessary to give the numbers for all the experiments, 

 but one or two typical cases may be quoted. 



A water extract from sycamore leaves had an activity of 45. When 

 shaken up with lead peroxide and then allowed to settle, the activity was 

 increased to 85. The rate of decay from this increased value was very slow. 

 An extract from leaves of an ash tree had a small activity of 12, which was 

 increased to 35 by treatment with potassium permanganate. An extract 

 obtained from horse-chestnut leaves had an activity of 40. This was only 

 slightly increased by potassium permanganate, but when treated with lead 

 peroxide the activity quickly rose to 90. After standing overnight the 

 activity had fallen very little, and when shaken up again with more lead 

 peroxide the activity was further increased. 



The large increases in photo-electric activity noted above, and also results 

 obtained when trying to isolate sulistances from the residues left when water 

 extracts of leaves were distilled off, led us to try the effects of oxidizing 

 agents on some organic substances. 



Hydroquinone in the solid state gave only a small effect when exposed to 

 ultra-violet rays, but a saturated solution in cold distilled water had an 

 activity of 40. When to the solution of hydroquinone a little paste, made 

 by shaking up lead peroxide with water, was added, the odour of quinone was 

 at once apparent, and the activity rose to 80. In a few hours the activity 

 had fallen away, but was restored by adding more lead peroxide. The 

 quinone which is produced is not specially active, and the lead peroxide is 

 inactive. It is clear, therefore, that the increased activity is connected with 

 the process of oxidation of the hydroquinone. 



