6-liS SUMMARY OF ODRIIENT RESEARCHES RELATING TO 



bent Uj)\varcl from the strip at an angle of 45°, and have a square bole 

 througb it. The film increases in brilliancy as it grows thin. The 

 light sboiikl be thrown on the film from above, so that the beam will be 

 refiuctcd up the tube of the instrument. The proper angle can readily 

 bo found by trial. 



The following are some directions for making suitable soap- 

 bubbles : — 



(1) Shave Marseilles (Castille) soap and dry thoroughly in the sun or 

 on a stove. (2) Put the dried sliavings in a bottle with alcohol of exactly 

 80 per cent, strength (sjiecific gravity 0*8G5), sufiicieut to form a 

 saturated solution at GO^ Fahr., the solution then marking 74° on the 

 centesimal alcoholometer, with a density of O'BBO. The solution must 

 be made cold, as warm alcohol would dissolve too much soap, and tho 

 solution would solidify when cool. 



(3) Make a mixture of glycerin 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 glycerin and water, and 

 it is well to heat the solution in a water-bath. 



(4) To make the final solution, take 100 part?, by volume, of tho 

 glycerin solution (3) to 25 parts of the soap solution (2), mix and boil 

 to expel alcohol. When cool, pour into a graduate and add water to 

 equal 100 volumes. Then filter several times to remove oleate of lime. 

 Common glycerin is af)t to make the solution turbid on account of the 

 presence of gyi)sum and lime. A funnel with a plug of cotton makes 

 the best filter, as the flow can be regulated by the tightness of the cotton 

 in the funnel. Soaji-bubbles, not more than 4 in. in diameter, and sup- 

 jjortcd 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. 



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



Dissolve one part of Marseilles soap in 40 parts of water (rain or 

 distilled), which may be warmed. When cool, filter through very porous 

 filter paper and add Price's glycerin in the proj^ortion of 11 parts of 

 glycerin to 15 parts of the soap solution. Shake thoroughly, and allow 

 the solution to stand for seven days where the temperature will not fall 

 below 67° Fahr. Then cool to 37° Fahr. and filter, keeping a bottle of 

 ice in the funnel. The first parts filtered should be refiltcred, using 

 very porous filter paper. Halbrook's brown oil silk soap, or his 

 Galli]ioli soap, and Sheering and Glatz's glycerin work very well. Long 

 standing and decantation from sediment may take the place of the second 

 filtration. After all the trouble, the mixture may not give very good 

 results. 



An excellent soap-bubble solution may be formed by a compound of 

 oleate of soda and pure glycerin. Bubbles 2 feet in diameter may be 

 blown, and bubbles have been kept under glass for 48 hours. 



A good and easily prepared solution may be made by shaving 4 oz. 

 of Marseilles, or better, of pure oil soap, and jilacing it in a quart of 

 distilled or rain-water. Shake until a saturated solution is formed, 

 and let it settle for a few hours. The solution should then be clear. 

 If otherwise, pour off the water, and add fresh water to the same soap 

 and try again. To the clear solution add about one-half the quantity of 

 glycerin that is absolutely pure. The presence of the least quantity of 

 acid in the glycerin is fatal to good results and therefore it is recom- 



