1S13.] emitted from the Lungs during Respiration. 345 



to B. After having stood some time, till it has acquired the 

 temperature of the surrounding air, the stop-cock, G> is turned, 

 and the elastic gum-bottle, D, containing a pretty strong solu- 

 tion of caustic potash, is screwed on at the bottom, as" repre- 

 sented, in such a manner that no air be suffered to exist in it. 

 The cock, H, is then turned, and the caustic potash introduced 

 into the instrument, and well shaken, till all the carbonic acid is 

 supposed to be absorbed ; it is then returned into the bottle, and 

 the stop-cock, H, secured. The instrument is then transferred to 

 the stand, F, and the cock, H, again opened under water in 

 the vessel, E, which rising shows the quantity of carbonic acid 

 contained in the analised air, care being taken to raise or depress 

 the instrument till the water stands exactly at the same height on 

 the inside as the outside of the stem. 



The bladder used on this occasion contained about 300 cubic 

 inches, and the number of expirations was always six, which were 

 made as nearly as possible in an uniform manner, both with 

 respect to time and depth. 



From some experiments made with mercury, and also ex- 

 pressly with the view of ascertaining the quantity of carbonic 

 acid absorbed by the water used in the experiment, I have reason 

 to conclude that the quantity, upon an average, amounted to 

 about one per cent. This quantity, accordingly, has been added 

 to all the numbers originally found by the instrument. As this 

 source of error was general and uniform, it is obvious that the 

 results were not comparatively affected by it. Other sources of 

 error, which I am well aware are very numerous, were carefully 

 guarded against by every possible attention to those circumstances 

 in which they were most likely to take place. 



Article III. 



On the Method of separating Iron from Manganese. By 

 Charles Hatchett, Fsq. F.H.S. &c. 



(To Dr. Thomson.) 



DEAR SIR, Mount Clare, Roetiampton, Sept. 25, 1813. 



In the last Number of your Annals of Philosophy I have 

 remarked a paper entitled " Contributions towards a Chemical 

 Knowledge of Manganese, by Dr. John," first published in 

 Gehlen's Journal fur die Chimie, &c. in which the author states 

 Gehlen's method of separating iron from manganese by succinic 

 *wd, and aUo hi* own process performed by means of oxalic 



