22 



106. Apparatus used in an investigation by Messrs. 

 Lawes, Gilbert, and Pugh, to determine whether plants 

 assimilate free or uncombined nitrogen. See Philo- 

 sophical Transactions, Part 2, p. 493, 1859 ; and Journal 

 of the Chemical Society, new series, vol. i. ; Entire 

 Series, vol. xvi., 1863. 



1876. Lent by Sir John Bennet Lawes, Bart. 



The tap being opened, and water allowed to flow from a 

 raised reservoir into the large stoneware Woulff's bottle, air 

 passes from it by the small leaden exit tube, through two glass 

 WoulfFs bottles containing sulphuric acid, then through the 

 long tube filled with fragments of pumice saturated with 

 sulphuric acid, and, lastly, through a Woulff's bottle containing 

 a saturated solution of ignited carbonate of soda ; and, after 

 being so washed, it enters the glass shade, from which it passes 

 by an exit tube through an eight-bulbed apparatus containing 

 sulphuric acid, by which communication with the unwashed 

 external air is prevented. Entering the shade at the side 

 opposite to this exit tube is a tube for the supply of water or 

 solutions to the soil, but which is at other times closed. In 

 front of the shade is a bottle connected by a tube with the 

 bottom of the earthenware lute-vessel, for the collection of the 

 condensed water, which is from time to time withdrawn from 

 the bottle by suction, and returned to the soil. The shade 

 enclosing the pot and plant stands in the groove of a specially 

 made, hard-baked, glazed, stoneware lute- vessel, mercury being 

 the luting material. Carbonic acid is supplied as occasion may 

 require, by adding a measured quantity of hydrochloric acid to 

 the bottle containing fragments of marble, the envolved gas 

 being, as will be seen, washed through one of the bottles of 

 sulphuric acid, through the long tube, and through the 

 carbonate of soda solution, before entering the shade. The short 

 leaden pipe, bent and opening downwards externally to the 

 large stoneware bottle, passes nearly to the bottom of it inside, 

 and is a safety tube for the overflow of the water when the 

 vessel is full, and so prevents it passing into the wash bottles, 

 &c. When full, the cork near the bottom of the stoneware 

 vessel is withdrawn, and the water flows by means of a drain 

 back into a tank, from which it is pumped into the raised 

 reservoir for re-use. It will be observed that, by the arrange- 

 ment described, the washed air is forced, not aspirated, through 

 the shade, and the pressure being thus the greater within the 

 vessel,the danger of leakage of unwashed air from without inwards 

 is lessened. In 1857 twelve sets of such apparatus were employed, 

 in ]858 a larger number, some with larger lute-vessels and 

 shades, in 1859 six, and in 1860 also six. The whole were 

 arranged side by side in the open air on stands of brickwork, as 

 indicated. 



