New Experiments with Soap Bubbles. 361 



iron saucepan, and mix it with about one-and-a-half times its 

 bulk of a strong solution of caustic soda; then heat it to 

 boiling for some time, keeping it well stirred. The oil will 

 thus gradually, by the action of the alkali, be converted into a 

 soap. The heating must be continued till all the oil has been 

 decomposed. This may be ascertained by dissolving a few 

 grains of the mixture in water, when, if any unconverted oil 

 be present, it will be seen to float. If after some time the oil 

 still separates, more soda must be added, and the boiling con- 

 tinued till the desired end is attained, some excess of soda 

 being always necessary. The mixture should then receive the 

 addition of an equal bulk of water, so as to bring it into 

 complete solution, and the whole allowed to cool, when a 

 quantity of white soap will separate from a clear liquid. This 

 soap should be strained and squeezed on calico, till no more 

 liquid can be pressed out. Then it must again be dissolved in 

 hot water, and a little more soda added, and allowed to cool. 

 It will now again separate, and must be pressed as before, till 

 the cake of soap is quite hard, when it will be pure enough for 

 making the solution. 



Should the foregoing process (which is less troublesome in 

 practice than its description appears to indicate) be found too 

 difficult, there is yet another plan which, though not quite so 

 successful, is far more easy. It is thus : — Shred finely 150 

 grains of Castile soap (which can be procured of any druggist), 

 and shake it up in a bottle with half a pint of distilled or pure 

 rain water until it is at length dissolved, then allow the turbid 

 solution to settle, and filter through blotting-paper. The clear 

 solution can then be used to mix with glycerine instead of that 

 of the pure oleate. 



I will now suppose a bubble made with our solution, and 

 successfully placed on its ring. It will after a few minutes 

 be glowing with gorgeous colours, which vary almost every 

 minute from the richest violet to the most brilliant orange. 

 Now darken the room. Then take some common spirit 

 (brandy will do) that has previously been shaken up with 

 some common salt, -and with it moisten some cotton wool, 

 which inflame. Now look at the bubble illuminated by the 

 yellow light thus produced. Instead of the former lovely 

 tinted sphere we see a yellowish thing, and on a closer inspec- 

 tion, we find that the parts formerly the brightest are now 

 marked by streaks and smears of a dead black, which are 

 shifting about continually. They are not beautiful certainly, 

 but are curious when we remember that they mark the lines 

 and surfaces of equal thickness where the yellow light, by reflec- 

 tion from the two surfaces of the film, is made to extinguish 

 itself, and produce the darkness. If instead of a salted spirit 



