^44 APPENDIX. 



This apparatus consists of a three-necked WoulfFs jar, of about 1,000 cc. 

 capacity. 



Into one of the necks is ground a tube (a), reaching nearly to the bottom, 

 which can be closed by a stop-cock, whilst the second neck is closed by a 

 glass-cock burette, divided into cc., and the third by a manometer. In the 

 lower part a cock is fixed, perforated in such a manner that the interior of 

 the bottle can be brought into connexion either with the open air by closing 

 the manometer, or with the manometer alone. 



The apparatus, the volume capacity of which has been previously ascer- 

 tained by weighing with distilled water, is thereupon filled with the gas to be 

 examined in such a manner as to allow the gas to flow in through the pipe 

 reaching nearly to the bottom of the jar, by means of a tube, whilst at the 

 same time the air in the apparatus escapes through the cock attached to the 

 manometer. When it is supposed that the jar has been completely filled 

 with the gas, first the outside air is shut off by means of the manometer cock 

 by which the same is brought into connexion with the interior of the jar, and 

 next the gas supply pipe. The difference of pressure occurring at the moment 

 the connexion is being shut off, which can be observed on the manometer, 

 must be equalised by carefully opening the manometer cock, whereupon the 

 gas can be tested as to the per-ceutage of carbonic acid contained in it. 



It is advisable, in order to remove the disturbing influence of the changes 

 in the temperature, to surround the glass jar with water of the same tempe- 

 rature as that of the room. After a lapse of three or four minutes at the 

 utmost, the interior of the jar with the surrounding water will have assumed 

 the same temperature, as can be easily ascertained by thermometers attached 

 within and without. 



The principle of determining the carbonic acid is, that the carbonic acid is 

 allowed to be absorbed by potash-lye, and then replaced by an equal volume 

 of potash-lye. 



By opening the glass-cock of the burette, some drops of potash-tye are put 

 into the jar. At the first moment the pressure will be increased, which, 

 however, is soon lessened by the absorption of the carbonic acid. There- 

 upon potash-lye is dropped in in the same quantity as the absorption of the 

 carbonic acid is consumed, so that the position of the indigo solution in the 

 manometer remains the same. 



Where the absorption of the carbonic acid is completed, it will be necessary 

 to wait for a few minutes, and in case there is still a difference of pressure, to 

 drop in so much of potash-lye that the manometer show again exactly its 

 first position. 



The volume of carbonic acid having been replaced by potash-lye, this 

 volume can be read on the burette. 



As the capacity of the jar is known, at Rudorff 's experiments with this 

 apparatus it contained 8 80 cc., there will be necessary of potash-lye : 



at 1 per cent, volume of carbonic acid 8 80 cc. 

 at 2 2-88 = 



at 3 3-88ec. 



In order to form a judgment on the exactness of this method, Eudorff filled 

 the jar with hydrogen and carbonic acid of known strength, and thus he 

 obtained : 



Found. Calculated. 



1 per cent. Co. 2 8' 7 cc. 8*8 



2 17-8 17-6 



3 26-8 20 '4 



4 35-1 05-2 



