548 



3. The conditions of atmosphere to be supplied to the plants, 

 and the means of securing them ; the apparatus to Ibe employed, &c. 



4. The changes undergone by nitrogenous organic matter during 

 decomposition, affecting the quantity of combined nitrogen present, 

 in circumstances more or less analogous to those in which the expe- 

 rimental plants are grown. 



5. The action of agents, as ozone ; and the influence of other 

 circumstances which may affect the quantity of combined nitrogen 

 present in connexion with the plants, independently of the direct 

 action of the growing process. 



In most of the experiments a rather clayey soil, ignited with free 

 access of air, well-washed with distilled water, and re-ignited, was used 

 as the matrix or soil. In a few cases washed and ignited pumice- 

 stone was used. 



The mineral constituents were supplied in the form of the ash of 

 plants, of the description to be grown, if practicable, and if not, of 

 some closely allied kind. 



The distilled water used for the final rinsing of all the important 

 parts of the apparatus and for the supply of water to the plants, was 

 prepared by boiling off one-third from ordinary water, collecting the 

 second third as distillate, and redistilling this, previously acidulated 

 with phosphoric acid. 



Most of the pots used were specially made, of porous ware, with a 

 great many holes at the bottom and round the sides near to the 

 bottom. These were placed in glazed stone- ware pans with inward- 

 turned rims to lessen evaporation. 



Before use, the red-hot matrix and the freshly ignited ash were 

 mixed in the red-hot pot, and the whole allowed to cool over sul- 

 phuric acid. The soil was then moistened with distilled water, and 

 after the lapse of a day or so the seeds or plants were put in. 



Very carefully picked bulks of seed were chosen ; specimens of the 

 average weight were taken for the experiment, and in similar speci- 

 mens the nitrogen was determined. 



The atmosphere supplied to the plants was washed free from 

 ammonia by passing through sulphuric acid, and then over pumice- 

 stone saturated with sulphuric acid. It then passed through a solu- 

 tion of carbonate of soda before entering the apparatus enclosing the 

 plant, and it passed out again through sulphuric acid. 



