1917] on Soap Bubbles of Long Duration 187 



The first item of Table 1 includes tlie first bubble (50 per cent, 

 glycerine, 5 per cent, ammonium oleate), which kept its colour instead 

 of developing- to blackness. This was caused by moisture left after 

 cleaning the 5-litre bottle in which it was blown ; no more moisture 

 than enough to give a bedewed appearance was left, bat this distilled 

 to different parts of the vessel, as the local temperature altered, and 

 resulted in a movement of water vapour sufficient to keep the 

 absorbent bubble thick enough to show colours. 



Sharply marked zones of different colours are a feature of such 

 bubbles. For this an undisturbed atmosphere is necessary ; other- 

 wise convection currents in the bubble will, by continual mixing, 

 prevent the quiet development of separate colour zones. The tem- 

 perature alterations must, therefore, be small. From the records of 

 one bubble the following appearances were noted : — 



On the 15th day. 20 cm. in diameter : sharp boundary line 

 at " 60° N. Lat." between steel-blue above and greenish-yellow 

 below : similar boundary between blue-green and blue-purple at 

 " 50° S. Lat." Large drop on bubble. 



On the 18th day. Diameter, 19*4 cm.: three sharp Une 

 boundaries : green to purple at " 30' X." : dark green to light 

 green at ^' 70"" S." : light green to thin magenta at " 80° S." : intense 

 green disc at lowest part. Drop fallen off. 



On the 2-l:th day. Main area of bubble fairly uniform red- 

 purple : boundary at " 75° N." to pale green above, and to deep 

 green below at ' 60° S." Graded Newton's rings of mauve and 

 green below this. 



The life of the bubble shown in the second item of Table 1 was 

 double that of those in the first item, namely, 98 days instead of 

 about 40 days. The solution used had 10 per cent, of ammonium 

 oleate instead of 5 per cent, as before. This factor, however, had 

 less influence than the generally lower temperature of under 11° C. 

 instead of up to 20° C. as before. Between the 75th and 95th days 

 there was a contraction from 11*4 cm. diameter to 10*4 cm., while 

 still remaining coloured. By the 95th day the bubble had become 

 too dilute to maintain any colour, and accordingly developed to the 

 thinnest or '• black " stage in the upper half. On the night of the 

 98th day the temperature of the Laboratory fell to near freezing 

 point, and the bubble did not survive this change. 



The next item refers to a bubble of 5 per cent, potassium oleate 

 in 50 per cent, glycerine. The 12-litre aspirator in which it was 

 blown was well dried, and, further, was placed in a vault where only 

 slow and small temperature variation occurs. In three months the 

 variation was from 9^ C. to 11° C. This solution was chosen because 

 of its property of giving extremely slow development to the " black " 

 stage. The result was that in 95 days the zone of black had only 

 extended down to " 25° S. Lat.," the remainder being so thick as 

 only to be feebly coloured with faint pink-and-green rings, probably 



