260 PROCEEDINGS OP THE AMERICAN ACADEMY 



If found tight, as indicated by the liquid in the potash bulbs, the tube 

 B is again turned up, and the substance then introduced in the manner 

 above described. A very slow stream of oxygen is now admitted ; the 

 tube B again turned down till the level of mercury in this tube shall 

 be half an inch to an inch below the level of mercury in the receiver 

 C ; and from time to time during the combustion the position of this 

 tube is adjusted so as to preserve about this difference between the levels 

 of the mercury, or at least so as to prevent the mercury in the tube 

 from ever rising above that in the receiver. 



In this manner the mercury, instead of offering resistance to the 

 passage of gas from the combustion apparatus, and thus increasing the 

 internal pressure upon the joints, which would be objectionable, actually 

 operates advantageously by producing partial exhaustion, and thus 

 diminishing the internal pressure upon the joints, and consequently the 

 liability to leakage. The distillation of the substance is now com- 

 menced, and conducted as previously detailed above. So soon as con- 

 densation of moisture appears in the neck of the chloride of calcium 

 tube, indicating that combustion has commenced, the flow of oxygen 

 may be gradually accelerated to keep pace with the progress of the 

 combustion, as indicated by the bubbles in the potash bulbs. When 

 the burning of the substance seems to have been completed, heat is 

 gradually applied, for a shox't time, along the whole length of the 

 column of asbestos, to obviate the possibility of any loss from unburnt 

 substance. 



The absorbing apparatus may be weighed filled with either oxygen 

 or air ; for myself, I prefer the latter, as, on the whole, more convenient 

 and less liable to lead to error. At the close of the analysis, therefore, 

 I expel the oxygen from the apparatus by admitting air from the air- 

 gasometer,* saving for further use the oxygen which is expelled during 



* The oxygen-gasometer and the air-gasometer each having a separate drying 

 apparatus, the time consumed in changing from one to the other is very much 

 shortened, as the necessity for displacement of the oxygen or air — as the case may 

 be — which is contained in the drying apparatus is avoided. Each drying apparatus 

 consists, 1st, of Liebig's bulbs, containing sulphuric acid; 2d, of a U tube, 15 inches 

 high (nearly 3 feet of tube), filled vpith soda-lime for carbonic acid ; and, 3d, of two 

 such U tubes (5 to 6 feet of tube), filled with chloride of calcium. The object in 

 using drying tubes of such large dimensions is to avoid the necessity of too frequent 

 renewal. The gasometers stand in a pan of copper, which is provided with an out- 

 let to the sink, so that they may be filled without disconnecting from the drying 

 apparatus ; thus giving a degree of permanence to the apparatus and saving some 

 labor. 



