430 NATURAL SCIENCE. June. 



fancied the poison miii^lit be a gas absorbed in the water and passing" 

 over in distillation. Carbonic acid, ammonia, and ozone were ruled 

 out of the question, as any water in which Algae live necessarily con- 

 tains these gases in greater or less quantit}', and such water, from spring 

 or river, pool or pond, was found to be harmless. Moreover, when 

 these gases were added to the cultures no effect followed. There 

 remained nitrous acid to be suspected, and the more so that Munich 

 water was said to contain a good deal of this acid which would not 

 be eliminated by distillation. A solution was made containing potas- 

 sium nitrite and sulphuric acid, which would liberate free acid in the 

 distilled water. The same results followed as before, namely, 

 chemical poisoning in the stronger solution, and the oligodynamic 

 effect when much diluted. Griess's test was applied to estimate the 

 quantity of nitrous acid in the ordinary water and in distilled water, 

 but only once was there any reaction, and that so slight that no 

 possible harm could be done by the amount present. 



Very remarkable results in rendering water oligodynamic were 

 obtained by treating it with various bodies considered practically 

 insoluble in ordinary water. These were copper, silver, lead, iron, 

 tin, and quicksilver. A whole series of experiments was tried with 

 well-cleaned coins. Thus glass vessels, containing loo or 500 cubic 

 centimetres of water, were arranged with one, two, four, and eight 

 gold coins. In these glasses were placed equal quantities oi Spirogyra 

 filaments. The plants in the glasses with the largest number of coins 

 died first, the others succumbed more slowly, while the same species 

 of Spirogyra lived in a healthy condition for weeks in ordinary 

 spring water. 



Again, the effect was tried with neutral water in metallic vessels 

 of silver and platinum ; the Spirogyra filaments died as before, and if 

 copper coins were dropped in a glass containing the filaments the 

 effect was so far localised that those nearest the coins were attacked 

 first. 



Niigeli had thus found an easy method of rendering water oligo- 

 dynamic. A step further, and he made the still more remarkable 

 discovery that he could again render the solutions neutral by the 

 addition of quite insoluble bodies, trying first sulphur, soot, or 

 graphite, then manganese, starch, flour, cellulose (filter-paper, cotton, 

 linen, or wood), silk, wool, stearin, paraffin, etc., and the more of 

 these bodies he put in, the quicker did the water recover its neutrality. 

 He found that Algae themselves would act in the same way if he put 

 in plenty of them ; they, too, had power to render the water neutral. 

 This enabled him to account for much that had been hitherto inex- 

 plicable in the control experiments, where no proportion had been 

 observed between the relative quantities of Algae and water. This 

 was put definitely to the proof, and it was found that the more water 

 used, and the fewer the filaments, so much the quicker did oligo- 

 dynamic reaction take place. Colloid substances, such as gum. 



