Soap Bubbles
and the Forces which Mould Them

THE FORCES WHICH MOULD THEM. 143 soap is very good, and this may be obtained from any chemist. Bubbles blown with soap and water alone do not last long enough for many of the experiments described, though they may some- times be made to succeed. Plateau added glycerine, which greatly improves the lasting quality. The glycerine should be pure ; com- mon glycerine is not good, but Price’s answers perfectly. The water should be pure distilled water, but if this is not available, clean rain- water will do. Do not choose the first that runs from a roof after a spell of dry weather, but wait till it has rained for some time, the water that then runs off is very good, especially if the roof is blue slate or glass. If fresh rain- water is not to be had, the softest water should be employed that can be obtained. Instead of Castille soap, Plateau found that a pure soap prepared from olive-oil is still better. This is called oleate of soda. It should be obtained freshly prepared from a manufactur- ing chemist. Old, dry stuff that has been kept a long time is not so good. I have always used a modification of Plateau’s for- mula, which Professors Reinold and Rücker