4 Mr. J. Y. Buchanan on an Apparatus for Gas-analysis, 



bottom. The mercury immediately rises in the tube ; and by 

 supplying its place in the cylinder and reducing the pressure in 

 A or B, as the case may be, the whole or part of the gas may 

 be transferred to the instrument. Of course in all these cases 

 the india-rubber tubes must be moistened inside with solution 

 of corrosive sublimate. 



The gas, having been introduced in one way or the other, is 

 brought all into the eudiometer q, mercury being allowed to run 

 over from A into q until the whole capillary part, down to where 

 it joins the eudiometer at g, is full of mercury, q is a short 

 eudiometer with a scale of only six divisions, like the measuring- 

 tube in Frankland's apparatus*. It is immersed in the cylinder 

 r, which is tilled with water. The legp is divided into millime- 

 tres, and is lowered or raised until the meniscus of the mercury 

 stands exactly at one of the lines. The difference in height of the 

 two columns is then measured by means of the millimetre-scale 

 on p, and the temperature of the water in r ascertained. These, 

 with the height of the barometer, give the volume of the gas. 

 On the tube r marks are made (not shown in the drawing) cor- 

 responding to and on the same level with those on q. When 

 the difference of level of the mercury in the two tubes is to be 

 measured, p is applied to r and the level of the mercury in q read 

 off, the marks on r giving the direction for the eye ; that in p is 

 then read off in the ordinary way, the difference giving the co- 

 lumn of mercury to be added to or subtracted from the baro- 

 meter-reading. 



Let us suppose that we have a sample of air extracted from 

 water. It consists of oxygen, nitrogen, and carbonic acid, the 

 last of which is determined first by absorption with caustic pot- 

 ash. For this purpose mercury is run out of n by means of y, 

 p is raised, and the stopcocks c, b, and a opened. The air is 

 thus drawn over out of q into m, mercury being allowed to fill 

 the capillary, when the cocks are again shut. The cup e is now 

 filled with strong solution of caustic potash, and, the level in n 

 being still kept low, the stopcock a is opened full, and then d very 

 carefully, caustic potash being allowed to run down through a 

 into m, where it meets the gas in the most advantageous way for 

 quick absorption. When enough caustic potash has been allowed 

 to enter, «?is closed, some mercury poured into e } d again opened 

 and the solution in the capillary replaced by mercury. When 

 the absorption is finished, the level of the mercury in n is again 

 raised and the stopcocks b and c opened. The stopcock a is now 

 very carefully opened, the flow of the gas being further regu- 



* The tube q in the figure is shown divided as stated in the text. I 

 have found, however, that it is much more convenient to have it divided 

 into millimetres ; and the labour of calibration is no greater. 



