504 



Profs. Liveing and Dewar. 



[June 10, 



acid into the flask was attended with a marked increase in the bright- 

 ness of the nitrocarbon bands, which died away again when the 

 current of gas was continued without fresh introduction of acid. On 

 testing the acid it was found to contain, as is frequently the case with 

 sulphuric acid, a small quantity of oxides of nitrogen. This quantity 

 was, however, so small that the amount of nitrogen introduced at each 

 introduction of acid must have been but a small portion of the amount 

 introduced in the bubble of air above mentioned, yet it gave a very 

 sensible increase in the brightness of the nitrocarbon bands. The 

 difficulty of getting all the air expelled from the apparatus led 

 us next to adopt a modification of this experiment. The carbonic 

 oxide was generated by heating in a tube of hard glass in an ordinary 

 combustion furnace a mixture of pure and dry potassium oxalate with 

 one quarter of its weight of quicklime, the mixture having been 

 previously heated for some time so as to expel traces of ammonia. 

 The rest of the apparatus was similar to that used in the previous 

 experiment, but in order to expedite the removal of the air the narrow 

 tube, b, was connected with a Sprengel pump, and the air exhausted 

 before heating the oxalate. The distant end of the tube with the 

 oxalate was then heated, and the whole apparatus filled with carbonic 

 oxide ; it was then again exhausted with the pump, refilled by heating 

 more oxalate, and the gas allowed to stream out through the pump for 

 some time. The heat was then lowered, sparks were passed and the 

 spectrum observed. No trace whatever of the nitrocarbon bands could 

 be detected, however the spark might be varied. The pump was now 

 set going again, and the pressure of the gas reduced to 1 inch of 

 mercury, while the spectrum was observed from time to time. Still no 

 trace of the nitrocarbon bands could be detected. More of the oxalate 

 was next heated, and the observations repeated again and again, 

 always with the same result. We came, therefore, to the conclusion 

 that carbonic oxide, if quite free from nitrogen, does not give, at the 

 atmospheric or any less pressure, the nitrocarbon spectrum, 



From Dr. Watts' account of his experiments, it appeared that he 

 had used carbonic oxide prepared by the action of sulphuric acid on 

 ferrocyanide, and it was probable that it might have been contaminated 

 with nitrogen, or with nitrogenous compounds, from the ferrocyanide. 

 We accordingly repeated our experiments with carbonic oxide so 

 prepared, and found that the nitrocarbon bands were then always 

 distinctly seen. 



We have also repeated Angstrom and Thalen's experiments with the 

 spark between carbon poles in nitrogen and carbonic acid gas. For 

 this we used a wide glass tube (fig. 7), to one end of which a quartz 

 lens, a, was cemented, while the other was stopped with a cork, through 

 which were passed two stout platinum wires with little cones of carbon 

 (6), purified in Bunsen's manner, fastened, as shown in the figure, on 



