1880.] in the Amount of Carbon Dioxide in the Air. 345 



The method of estimation which I employed consisted in absorbing 

 the carbonic acid from a known volume of air by means of baryta 

 water of known strength, the amount of carbonic acid so absorbed 

 being determined by titrating the alkaline fluid with a standard acid 

 solution, 1 cub. centim. of which was approximately equal to 1 mgrm. of 

 CO.-,. This method is generally known as Pettenkof er's, but it is worth 

 noting that it had been used by Dalton as far back as 1802.* It is 

 particularly well adapted to the end I had in view, for it is not 

 merely the most expeditious of the processes hitherto devised, but it 

 allows of the observations being made under strictly comparative 

 conditions. 



The observations to which this communication refers were made in 

 a garden at Grasmere situated at the foot of a hill some 1,300 feet or 

 1,400 feet high, and which lies only a few feet above the level of the 

 adjacent lake, which is 208 feet above that of the sea. 



They were commenced on the 21st July and continued to the 25th 

 October; the whole summer and autumn being of an exceptionally 

 wet and sunless character. It was originally intended to pursue the 

 observations " de die in diem " until a sufficient number were obtained 

 to furnish a trustworthy average for comparison ; but the weather 

 proved such as to render this, if not impracticable, at least undesir- 

 able owing to the difficulty, especially at midnight, of filling the jars 

 with air in the open without at the same time admitting a few drops of 

 rain also, even although the greatest care was used in the operation. 



Whenever, therefore, any such danger owing to the state of the 

 weather seemed imminent, and that there was therefore a chance of 

 the error so occasioned creeping into the experiments, the observation 

 for the particular time was abandoned. In some instances by slightly 

 varying the times chosen for the observations (noon and midnight) it 

 was found possible to include some that otherwise must, for the fore- 

 going reason, have been omitted. And, with but few exceptions, the 

 slight differences as to time observable in the accompanying tables are 

 to be attributed to this cause. 



The place chosen for collecting the air for examination was a nook 

 on the lawn upwards of 100 feet from the house and almost 

 entirely surrounded by trees, shrubs, and flowers ; the plants being 

 chiefly the following, namely : pine, yew, holly, laurel, hawthorn, 

 mountain ash, rhododendron, geranium, rose, phlox, and azalea. 



The air was taken at from four to five feet from the ground and 

 always, with one or two exceptions noted in the tables, at the same 

 place. On two or three occasions it was taken near a conservatory, 

 by well lighting the interior of which it was possible to dispense with 

 the lamp otherwise employed when filling the jars at night ; and thus 



* Dr. Angus Smith, " Air and Earn," p. 448 et seq. 



