J. H. Gilbert— Points in connection with Vegetation. 109 



are fully described in the papers already referred to, published 

 in the Philosophical Transactions for 185ft, and in the Journal 

 of the Chemical Society in 1863. They may be briefly de- 

 scrihed as follows: — 



The soils used were ignited, washed, and re-ignited, pumice, 

 or soil. The specially made pots were ignited before use, and 

 cooled over sulphuric acid under cover. The pots, with their 

 plants, were enclosed under a glass shade resting in the groove 

 of a specially made hard-baked glazed stone-ware lute-vessel, 

 mercury being the luting material. Under the shade, through 

 the mercury, passed one tube for the admission of air, another 

 for its exit, and another for the supply of water or solution* to 

 the soil ; and there was an outlet at the bottom of the lute- 

 vessel for the escape of the condensed water into a bottle 

 affixed for that purpose, from which it could be removed and 

 returned to the soil at pleasure. A stream of water being 

 allowed to flow into a large stone-ware Wolff's bottle (other- 

 wise empty), air passed from it through two small glass Wolffs 

 bottles containing sulphuric acid, then through a long tube 

 filled with fragments of pumice saturated with sulphuric acid, 

 and lastly through a Wolff's bottle containing a saturated solu- 

 tion of ignited carbonate of soda; and, after being so washed, 

 the air ente from which it passes, by the exit 



tube, through an eight bulbed apparatus containing sulphuric 

 acid, by wh i with the unwashed external air 



is prevented. Carbonic acid is supplied as occasion may re- 

 quire, by adding a measured quantity of hydrochloric acid to 

 a bottle containing fragments of marble, the evolved gas being 

 passed through one of the bottles of sulphuric acid, through 

 the long tube, and through the carbonate of soda solution, 

 before entering the shade. 



It will be observed that, by the arrangement described, the 

 washed air is forced, not aspirated, through the shade, and the 

 pressure being thus the greater within the vessel, the danger of 

 >i unwashed air from without inward is lessened. In 

 1857, twelve sets of such apparatus were employed ; in 1858 a 

 larger number, some with larger lute-vessels, and shades; in 

 1869 mx, and in 1860 also six. The whole were arranged, side 

 by side, in the open air, on stands of brick-work, as ,. 

 in the papers referred to, and shown in the apparatus 

 Drawings of some of the plants grown were also exhibited, and 

 the published results are summarized in Table VIL 



