84 
PEOEESSOE TYNDALL ON THE ABSOEPTION AND 
Several kinds of tea, treated in the same manner, produced absorptions which varied 
between 20 and 28. 
In the teas, cinnamon, musk, and the odorous plants already referred to, dry air had 
been passed over them for some time before they were examined. Still a small amount 
of aqueous vapour may have entered with the odours, and thus rendered the results to 
some extent of a mixed character. 
§ 10. Ozone. 
In my last memoir I alluded briefly to the action of ozone ; but the experiments then 
made having been executed with a brass tube, I was very desirous of repeating them 
with a tube which could not be attacked by this extraordinary substance. Experiments 
with the glass tube, performed on the 16th, 17th, and 18th of last July, satisfied me that 
I had not over-estimated its power as an absorber of radiant heat. 
In my first experiments I made use of large electrodes for the purpose of lessening 
the resistance to the passage of the current through the decomposing liquid. The 
oxygen thus obtained differed but little from ordinary oxygen. 
This year I had three decomposing vessels constructed ; in the first (No. 1) the pla- 
tinum plates had about four square inches of surface, being rolled up to economise 
space ; the plates of the second (No. 2) had two square inches of surface, while those of 
the third (No. 3) had only a square inch of surface each. Numerous experiments with 
these gave me the following constant results. Calling the absorption of ordinary 
oxygen 1,— 
Electrolytic Oxygen. 
Erom plates Absorption. 
No. 1 20 
No. 2 34 
No. 3 47 
A series of experiments made on the following day gave these results : — 
No. 1 21 
No. II 36 
No. Ill 47 
I now cut away a portion of the plates of No. II. so as to make them smaller than 
those of No. III. The oxygen obtained with these plates gave an absorption of 
65, 
thus exceeding No. III. considerably. The plates of No. III. were now reduced so as 
to make them smallest of all ; the oxygen which they delivered gave an absorption of 
85. 
I feared the development of heat with these smallest plates, and knowing heat to be 
very destructive of ozone, I surrounded the apparatus by a mixture of pounded ice and 
