392 On an Apparatus for Gas-analysis 



which it is packed when out of use, forms its support, and a 

 working tray for saving spilled mercury, when in use, were not 

 contemplated from the beginning, but suggested themselves 

 only after the glass work was finished, as until then the form 

 and size of the case could not be determined on. It was made 

 for me by Messrs Kemp and Co., of Edinburgh; and the 

 workmanship is in every way satisfactory. 



The apparatus consists essentially of two U -tubes. The 

 one, which, according to precedent, we may call the "laboratory 

 tube," is wholly of glass; the other (the eudiometer) has the 

 legs, of glass, united by an india-rubber tube of suitable length. 

 These are affixed to mahogany boards A and B, which fit into 

 the wings of the box C, where they are secured, each by two 

 bolts (z, z), passing into the sides of the box. D is a strong 

 mahogany box for holding mercury. 



The glass U-tube, which, for convenience, we shall call A, 

 as well as the board to which it is attached, is 0-42 metre high ; 

 the shorter leg is 0-18 metre from the bend to where the capil- 

 lary tube is joined on, and its diameter is 0-02 metre. The 

 diameter of the capillary tubes is 0-003 metre. In the U-tube 

 B, the eudiometer (q) is 0-17 metre from capillary to india- 

 rubber; the movable leg (p) is 0-34 metre long; and the 

 diameter of both is the same as in A . The length of the box C 

 is 0-45 metre, and the width and depth of each wing 0-195 metre 

 and 0-105 metre respectively. The mercury-box D measures 

 0-12 metre by o-io metre by 0-08 metre, and when in use fits 

 into the place where it is represented in the figure. When 

 dismounted it is not packed in the case with the rest of the 

 instrument. 



When in use, the parts A and B are screwed to the back of 

 one wing of the box, A with one, and B with two screws (x, x, x). 

 The back of the box carries four nuts, so that A may be fixed 

 to it close up to the end of the box and with the stopcock y 

 projecting over the side, leaving a space between A and B, the 

 object of which will be explained further on. 



The different parts of the apparatus will be best explained 

 by describing the manipulations, occurring during the analysis 

 of a gas, as well as those necessary for introducing the gas into 



