Speedy Volumetric Determination of Carbonic Acid. 185 



when they are made to point to the corresponding lines on the scale. 

 Should the pointer of one bell- jar meet say the middle line on the 

 scale, and the middle line on the scale of the other be above the 

 corresponding pointer, that bell-jar will have to be depressed by 

 working the screw until the middle line on its scale also corresponds 

 with the pointer. This can be done without any trouble, and has 

 seldom to be repeated the same day, while, at times, days elapse in 

 succession without necessitating this correction. 



The Absorption-tube. — Various descriptions of absorption-tube were 

 tried before I obtained it in its present form. It has to fulfil two 

 conditions, viz. : it must first of all absorb all the carbonic acid, secondly 

 give out no water. My present arrangement, which works very well, is 

 as follows : a straight hollow cylinder, 2 feet 3 inches in height, made of 

 thin sheet copper and silvered inside, is jacketed and surrounded with 

 glycerine over which floats a thin layer of oil to prevent the absorp- 

 tion of water. The cylinder is filled with fragments of pumice-stone 

 in the midst of which is inserted a long metallic tube. The cylinder 

 is closed with an india-rubber cork, perforated, through which is 

 inserted a glass "["-piece inverted. A very delicate thermometer di- 

 vided into tenths of a degree Fahrenheit is run through the upper 

 tube of the "P~piece into which it fits air-tight, while the horizontal 

 limb is placed in communication with the left-hand bell- jar by means 

 of india-rubber tubing. The thermometer has a very long stem, and 

 its bulb reaches far down into the metallic tube in the midst of the 

 pumice-stone, thus registering the temperature of the air in the absorp- 

 tion-tube. The space left between the fragments of pumice-sfcone 

 measures 1600 c.c. A narrow U~ sna P e( l glass tube connects the copper 

 cylinder with another wider vertical glass tube, the latter being filled 

 with pieces of caustic potash, and into it a narrow glass tube is fitted 

 air-tight with an india-rubber stopper; the latter is jacketed, the 

 annular space being filled with water. Thus the heat formed by the 

 combination of the carbonic acid with the alkali distributes itself 

 throughout the absorption- tube, and is prevented from reaching the 

 right-hand bell-jar by the water in the jacket which absorbs it on its 

 way. The U- sua P e( ^ tube connecting the vertical portions of the 

 absorption apparatus has a tube soldered to its lower part and 

 widened into a bulb, an arrangement the object of which is to drain 

 out the alkaline fluid after it has done flowing over the fragments 

 of pnmice-stone ; the tube beyond the bulb is finally closed with 

 india-rubber tubing and a pinch-cock. 



The alkaline fluid for the absorption of the carbonic acid consists 

 of half its volume of a saturated aqueous solution of potassium 

 hydrate, and half its volume of pure glycerine, and the mixture is 

 made to dissolve as much caustic potash in sticks as it will take 

 up. An excess of the alkali is invariably left in the fluid, so that 



