II. TEACHING (PURE). 509 



and the disposition to light within prevented. In the ordinary half-inch 

 burner one and a quarter volumes is about the maximum quantity of air which 

 may safely be mixed with the gas previous to combustion without running 

 the risk of lighting within. In the new burner 6-4 volumes of air may be 

 safely mixed previous to combustion. 



By raising or lowering the cap the proportion of air drawn in at the base 

 of the burner may be varied at pleasure, and when the maximum amount of 

 air is used a flame of marvellous beauty is obtained, which differs in many 

 respects from the ordinary atmospheric flame. The hollow conical space 

 within the flame entirely disappears, leaving a perfectly solid flame, while 

 above each perforation of the cap is seen an intensely brilliant green bead, 

 indicating the beginning of combustion. These beads are hollow, and filled 

 with the mixture of air and gas passing through the cap. Their colour is 

 entirely on the surface, and they fade and merge into each other on a slight 

 interruption of the air supply below. They cannot be regarded as separate 

 flames, as they have no separate air supply, and their colour is the same 

 whether the cap be of copper or iron. 



As the pre-admixture of air increases the flame becomes smaller and more 

 intense ; the heat is produced in less space, and is thus better adapted for 

 boiling liquids or heating metals. The absence of the hollow cone points to 

 some interesting peculiarities in the flame. In a flame 3" diameter from a 

 2" burner the green beads (those most sensitive indices of any change in the 

 physical condition of the flame) are of the same size and colour from the 

 outer edge to the middle. They are all filled with the same mixture of gas 

 and air, and their uniformity can only be accounted for by supposing that 

 each one gets its complement 'of air with equal facility. 



About 6^ volumes of air are necessary to consume London gas, and one half 

 of this amount will produce a carbonic oxide flame. But when 4-^ volumes 

 are mixed previous to combusion there is more than the amount required to 

 produce a carbonic oxide flame ; this fact, together with its uniform appearance, 

 offers grounds for supposing that the flame is a carbonic acid one, and that 

 the oxygen which combines during combustion reaches every part of it with 

 equal facility. The penetrating power of the oxygen is here so remarkable 

 that the question naturally arises, " does it drag its associated nitrogen with 

 " it into the heart of the flame, parting only at the time of combination, or, 

 " does dissociation take place before the oxygen combines with the cai'bon 

 ** and hydrogen of the gas ? " 



2448. Models of Hydrochloric Acid Condensing 

 Towers, as erected at Messrs. Hutchinson's Alkali Works at 

 Widnes. Professor Roscoe, F.R.S. 



2449. Model of Salt-Cake Furnace, with open roaster. 



Professor Roi>coe, F.R.S. 



2450. Model of Finishing (Alkali) Furnace. 



Professor Roscoe, F.R.S. 



2450a. Models of Stoneware Distilling Apparatus as 

 used by Manufacturing Chemists, and others, and comprising 

 still, still head, false arm, dip arm, condensing worm, three 

 receivers with connecting pipes and taps, mixing pan, and stone 

 jar. Made of improved vitrified stoneware, and warranted to 

 resist the action of the strongest acids. 



James Stiff fy Sons, London. 

 2450b. Model of Hoffman's Patent Kiln. 



Hermann Wedekins. 



