OF ARTS AND SCIENCES : MARCH 8, 1864. 255 



quired ; the supply of oxygen only requiring attention. In the ordinary 

 way, on the contrary, in which the heat is applied only on one side of 

 the substance, the latter, if volatile, is constantly changing position 

 backward in the tube, necessitating a corresponding movement of the 

 heat in the same direction ; which requires constant care and consider- 

 able skill. 



This procedure — referring to the immediate expulsion of liquid 

 from the bulb, etc. — implies that that portion of the tube immediately 

 forward of the bulb should not already be too warm, which might easily 

 be the case with a body of very low boiling-point. It would then be 

 necessary to expel the substance from the bulb no faster than the 

 oxygen would absorb it in the proper proportion ; which, as experience 

 has shown, may be easily accomplished. 



With a body of extreme volatility it may be also necessary to place 

 a dish containing pieces of ice under the bulb ; as even the temperature 

 of the surrounding air might in such a case cause the substance to 

 pass forward too rapidly. 



3. The oxygen is admitted through Liebig's potash bulbs contaming 

 sulphuric acid ; and the carbonic acid formed is absorbed by similar 

 bulbs with potash ; to which is attached a tube filled with soda-Hme 

 and chloride of calcium, as recommended by Mulder,* to take up any 

 traces of carbonic acid which may escape absorption in the bulbs, and 

 the trace of moisture which is invariably carried forward from the 

 latter. Special care should be taken to select both sets of bulbs with 

 the view to have the openings in the one as nearly as may be of the 

 same size as those of the other, so that the bubbles of oxygen, 

 considered as representing volumes, entering the sulphuric acid 

 bulbs, may be readily compai-ed with the bubbles or volumes of 

 carbonic acid entering the potash bulbs ; these bubbles may then serve 

 as a valuable index by which to regulate the supply of oxygen. 

 Especially is this true in cases where the composition of the body to 

 be analyzed is pretty nearly known, as then the number of bubbles 

 of oxygen required for every bubble of carbonic acid produced may 

 be readily calculated. 



But as it is, in any case, advisable to conduct the experiment so that 

 there shall always be an excess of oxygen passing unabsorbed through 

 the potash bulbs, and as this excess would seldom be large even 



* Liebig and Kopp's Jahresbericht, 1858, p. 588. 



