1888.] MICROSCOPICAL JOURNAL. 81 



Soap-bubble solutions and a slide for observing soap-bubble films.* 



By F. T. chapman, 



WASHINGTON, D. C. 



A simple means for showing soap films, by means of the microscope, may 

 consist of a thin strip of wood (3 in. by i in.) , or other material, with a metal 

 plate secured to it. The plate should have one end bent upward from the 



Fig. I. — Slide for Soap Films. 



strip, at an angle of about 45'^, and have a square hole through it. The film 

 increases in brilliancy as it grows thin. The light should be thrown on the 

 film from above, so that the beam will be reflected up the tube of the instru- 

 ment. The proper angle can readily be found by trial. 



Following are some directions for making soap-bubbles : — 



I. Shave Marseilles (castile) soap and drv thoroughly in the sun or on a 

 stove. 



IL Put the dried shavings of soap in a bottle with alcohol of exactly 8o"o 

 strength (specific gr. 0.865), sufficiertt to form a saturated solution at 60^ 

 Fahr., the solution then marking 74° on the centesimal alcoholometer, with 

 a density of 0.880. The solution must be made cold, as warm alcohol wooild 

 dissolve too much soap, and the solution would solidify when cool. 



IIL Make a mixture of glycerine and water, so as to mark 17.1° Baume, 

 or have a density of 1.35 at 68° Fahr. This solution can be made of equal 

 parts of the most concentrated glycerine and water, and it is well to heat the 

 solution in a water bath. 



IV. To make the final solution, take 100 parts, by volyme, of the glycerine 

 solution (III) to 25 parts of the soap solution (II), mix and boil to expel al- 

 cohol. When cool, pour into a graduate and add water to equal 100 vol- 

 umes. Then filter several times to remove oleate of lime. | 



Plateau's soap-bubble solution is prepared as follows : — 



* Read before the Washington Microscopical Society at its 72d Meeting. 



t Common glycerine is apt to make the solution turbid on account of the ))resence of gypsum and lime. 



A funnel with a plug of cotton m^kes the best filter, as the flow can be regulated by the tightness of the cotton 

 in the funnel. 



Soap bubbles, not more than four inches in diameter, and supported on a tripod under a bell-glass, are said to 

 last for an hour. 



The preparation is suitable for Plateau's experiments with thin films, soap bubbles, &c. From Pcggendorff's 

 AnnaJen., Scientific American, vol. 35, page 127, Aug. 26, 1876. 



