the film, and then breaking the film within the loop. What happen- ? 



i^S. hip a camel'- hair hrn-h in water; notice how it spreads 

 nit mi tile water hut clo-e- U|> when taken out. What pulls the 

 lri-tle- together? 



1^0. Cses made <>f surface film l>\ ori/anisms. ( >bscrve any of 

 the following for which there is an opportunity: Spiders, 

 "whirligig-". ! other animal- moving on the upper surface of the 

 water; tlatwnn- or -nail- creeping on the under -urface of the 

 film. 



n>K.MS OF FLUDS I'RoDL'CKI) I'.V SURFACE 

 PENSK 'X. 



1411. f'latean's experiment. Half till a gla.-s tumhler with 

 alcohol. With a pipette drop a few drop- . f olive oil into 

 tin- ; notice that they -ink. ( If they do not. add a -mall quantity of 

 ! alchol. i Xo\\- add a certain amount of 50' < alcohol -^'ithont 

 stirriin/. The drop- will lie found not to -ink to the bottom. If 

 nece--arv add more 50' , alcohol : or, if the drops do not sink at all, 

 add -ome 70'. alcohol. When a mixture has been obtained where 

 the drop- -ink part way but not to the bottom, it is ready for obser- 

 vation. What form do the drops take? Add a considerable 

 quantity of olive oil with the pipette, until a sphere an inch or more 

 in diameter i- produced. Why does it retain the spherical firm? 

 Try changing the -hape with a glass rod; doe- it return to the 

 -pherical form? Why doe- such a ma-- not keep the -pherical 

 lorm when placed on a Hat -urface? Place a drop of olive oil on 

 water and note it- -hape. 



I'KINVII'LK <>l ; LEAST < >K MINIMAL SURFACES. 



< >wing to the pulling . f the surface film in all direction- the 

 surface "f <> fluid tends to hccome as small as possible under the 

 liinitin,/ conditions. 



i-Ji. I lie -pherical form of the oil drop- or a -oap bubble ex- 

 emplifies tin'-. Why do they take the -pherical form? 



i J-'. In a di-k of paraffin oil floating <.n 70', alcohol, increa-e 

 the -urfare by pulling out |irojections with a gla-s rod. \\bat 

 happen- to the-. 



i (.v I- \amine a film of -oa|> -olution on a circular wire frame. 



Xou- that it i- Hal. Why? Now bend the frame in the form of 



op curved at right angle- to the radii of the loop. 



.hat i- the f. inn of the film on -uch a loop? Kxplain in term- of 



the principle. 







