iS73- 



Light. 



421 



the bead to remain a dark purple when cold, and exhibiting the complete 

 spectrum of Fig. 2. When 25 per cent has been added a blue bead results, 

 and the spectrum in Fig. 2 changes ; the band marked (3 is perceptibly lowered, 

 overlapping d, as in Fig. 3, but the band y remains as in Fig. 2. If 5 per cent 

 more is taken up, the three absorption-bands are like those drawn in Fig. 3, 

 which represents cobalt dissolved in borax. The bead is now very dark, and 

 requires pressing, whilst hot, between the points of the forceps, to render it 

 sufficiently diaphanous. In these experiments it is necessary the amount of 

 cobalt should be known when added to the weighed boric acid bead, since the 

 determination of the alkali is affected by the quantity of oxide present; 

 e.g., if enough cobalt has not been dissolved, it may require 17 J per cent 

 of sodium carbonate to render the band visible in the red of Fig. 2. 

 Fig. 4 represents the spectrum of a salt of magnesia when moistened 

 with a solution of cobalt. Fig. 5 is the spectrum of the indigo-blue com- 

 pound of calcium oxide when treated with cobalt. Fig. 6 is the interesting 

 spectrum of the bright blue compound of alumina. The beautiful green 

 compound of oxide of zinc, which is occasionally used as a pigment, 

 and known as Rinman's green, gives the spectrum pourtrayed in Fig. 7. 

 When a thin soda bead is formed with a mere fragment of boric acid, and 

 fused along with a little cobalt, in the outer flame, the bead while hot is 

 of a deep orange-brown colour, turning nearly black and opaque on cooling, 

 but before becoming quite cold rapidly crystallises and turns green. By 

 transmitted light the whole of the blue is cut off and part of the red, 

 while a narrow band is visible at the yellow end of the green. If the 

 bead, however, be submitted to the action of the inner flame, it turns a 

 pale blue while hot, and crystallises on cooling to a pale pink by trans- 

 mitted light, assumes a lavender tint by reflected light. This unique 

 spectrum of the pink bead is depicted in Fig. 8 ; and Fig. 9 represents 

 the flame spectrum of boric acid, consisting of four bright bands. 



Mr. George J. Warner, F.C.S, calls attention to the peculiarly sensitive 

 character of Wallace's gas-burner. It consists of a hemispherical chamber, 

 into which the gas is introduced through a cone fixed horizontally at a tangent, 

 the position of the jet with regard to the cone being so adjusted that the 

 quantity of air injected by the velocity of the gas at all ordinary pressures is 

 always the proportion required for its perfect combustion. The upper part of 

 the interior of the chamber is lined with wire gauze, and from it issue one 

 or more tubes, at which the gas is burned. At ordinary pressures the flame is 

 of the colour of a Bunsen burner, but with a central cone, clearly defined, of 

 pure green, whether it be turned high or low. But if the gas be reduced 

 below the ordinary pressure on the main, the flame becomes white-tipped, and 

 there is no longer perfect combustion, as in a defective Bunsen. We then find 

 that the flame is sensitive to sound, to all sound in fact, but to high notes 

 particularly. 



Microscopy. — Mr. H. C. Sorby has obtained from Aphides an orange- 

 coloured fluid, which he names aphidirholeine, giving a very remarkable 



B C D E b F 



G 



| | 



■ II I I 





1 : 1 



y m ill iiiiiHH 



spectrum. A narrow band in the orange, having the D line in its centre, 

 another close to the upper edge of the first band of nitrate of didymium, a 

 third a little above E, the general absorption towards the blue commences 

 about midway between b and F, and becomes stronger near the fifth band of 

 nitrate of didymium. The band in the orange is a singular and unexpected 

 phenomenon in a fluid of the same colour. 



vol. in. (n. s.) 3 1 



