96 Mr. D. Waldie on Combustion and Flame, 



part of the flame, and so different when projected on the upper 

 part, where the gas being ah'eady mixed with air it can act 

 only as a mechanical agent. 



This may be seen very well with sulphur. A crucible of 

 moderate size was filled to about one third with sulphur, and 

 placed on a charcoal fire till it boiled. A jet of oxygen flow- 

 ing with a certain force was introduced within the upper part 

 of the cavity of the crucible, entirely within the blue burning 

 flame of the sulphur outside; a strong yellowish tapering flame 

 was observed, darkish in centre, and red at edges and tail, of 

 about one inch in length. The same experiment was repeated 

 with the same circumstances, substituting air for oxygen; a 

 very slender jet of blue flame was observed darkish at centre, 

 and red at the tail, greatly smaller than that of the oxygen. 

 These flames are of course expanded by the heat of the va- 

 pour to double their volume, but their relative size is in ac- 

 cordance with the principles already laid down. 



The influence of quantity is also well seen when diluted 

 gases are burnt from a jet. Thus 1 oxygen and 8 nitrogen 

 or carbonic acid will not burn in the flask filled with hydro- 

 gen from the brass jet commonly used, nor even from the to- 

 bacco pipe, but will do so from the mouth of the flexible tube 

 about one-fifth inch diameter, forming a thin blue hollow cone 

 of flame, fig. 6 ; sometimes this cone was deficient at the top, 

 and was extinguished when the gas was made to flow with 

 greater velocity. 



In these cases when the diluted gas issues from a small 

 orifice the heat produced from the combustible mixture of the 

 gases is so little that it is cooled by the velocity of the cur- 

 rent ; from a larger orifice it comes more slowly, and the small 

 quantity of combustible mixture formed constitutes the thin 

 shell of flame observed. 



These then seem to be the primary causes regulating the 

 size and appearance of flames, hitherto, so far as I am aware, 

 unobserved or undescribed. Probably, however, these are 

 not the only causes, particularly with compound gases. I 

 have made a few observations on these, and have observed 

 some peculiarities, in nitrous oxide for instance; to these 

 however I shall not advert until they have been examined 

 more particularly. One peculiarity in the flame of hydro- 

 gen must have been frequently observed, namely, a green 

 jet inside of the usual dark central portion ; and when the 

 flame is full, a dark central part even in this. Having 

 only unsupported conjecture to offer in explanation of this, 

 I shall refrain from saying anything at present. There are 



