549 



Carbonic acid, evolved from marble by measured quantities of 

 hydrochloric acid, was passed daily into the apparatus, after passing, 

 with the air, through the sulphuric acid and the carbonate of soda 

 solution. 



The enclosing apparatus consisted of a large glass shade, resting in 

 a groove filled with mercury, in a slate or glazed earthenware stand, 

 upon which the pan, with the pot of soil, &c., was placed. Tubes 

 passed under the shade, for the ingress and the egress of air, for the 

 supply of water to the plants, and, in some cases, for the withdrawal 

 of the water which condensed within the shade. In other cases, the 

 condensed water was removed by means of a special arrangement. 



One advantage of the apparatus adopted was, that the washed air 

 was forced, instead of being aspirated, through the enclosing vessel. 

 The pressure upon it was thus not only very small, and the danger 

 from breakage, therefore, also small, but it was exerted upon the 

 inside instead of the outside of the shade ; hence, any leakage would 

 be from the inside outwards, so that there was no danger of unwashed 

 air gaining access to the plants. 



The conditions of atmosphere were proved to be adapted for 

 healthy growth, by growing plants under exactly the same circum- 

 stances, but in a garden soil. The conditions of the artificial soil 

 were shown to be suitable for the purpose, by the fact that plants 

 grown in such soil, and in the artificial conditions of atmosphere, 

 developed luxuriantly, if only manured with substances supplying 

 combined nitrogen. 



Passing to the subjects of collateral inquiry, the first question con- 

 sidered was, whether plants growing under the conditions stated 

 would be likely to acquire nitrogen from the air through the medium 

 of ozone, either within or around the plant, or in the soil ; that body 

 oxidating free nitrogen, and thus rendering it assimilable by the 

 plants. 



Several series of experiments were made upon the gases contained 

 in plants or evolved from them, under different circumstances of 

 light, shade, supply of carbonic acid, &c. When sought for, ozone 

 was in no case detected. The results of the inquiry in other re- 

 spects, bearing upon the points at issue, may be briefly summed up 

 as follows : 



