196 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lviii. 



plumula was of a pale yellow colour iu the corns grown in 

 obscurity, the colour of the same part in the corns grown 

 under the influence of light was a dark green. 



Xot being satisfied with the results already obtained, I 

 resolved to try a different method of experiment. I thought 

 that if the observations could be made volumetrically as to 

 the amount of carbonic anhydride produced, greater accuracy 

 might be attained. With this object in view I devised 

 and fitted up an apparatus similar in principle to that em- 

 ployed by Dr. Pauchon, and alluded to on a previous page. 

 There is, however, considerable difference in the details and 

 in the manner of experiment. 



n® ^==^ 



Fisr. 3. 



Description of the Apparatus, Fig. 3. — A, a large 

 strong glass tube (about 140 c.c. capacity) closed at one 

 end. The open end of the tube is closed by an india- 

 rubber cork, C. This cork is always pushed in to the same 

 distance, shown by marks scratched on the glass tube. 

 The cork has three perforations to carry three tubes, D, E, 

 and F. D has an internal diameter of 8 M.M., and is bent 

 in the form shown in the figure. It is graduated on both 

 limbs from to 9 m.m. E and F are two capillary tubes ; 

 F reaches nearly to the end of the tube A, while E is ter- 

 minated level with the inner surface of the cork. The 

 upper ends of both these tubes are closed by stoppers 

 covered by a water joint. Their use is for replenishing the 

 air in the large tube as often as it is considered necessary. 

 B and B^ are two porcelain spoon boats ; B contains a 

 measured quantity (about 1-3 c.c.) of distilled water, and 

 B^ about the same amount of potassa solution. The corns 

 experimented upon are placed near the closed end of the tube. 



