i ;o. I 'lace a small piece of camphor on the surface of clean 

 water. Result? Kxplain movements. What determines the direc- 

 tion of the movements? Touch the surface with a rod containing 

 a trace of >il. Kxplain what happens. 



151. ('//(/ m/t\v of form due to chemically induced chaiii/es of 



surface tension. Place a g 1 -i/ed drop of mercury in a watch- 



gla--; n te its form and size; now cover with 2' < IIN<>.; any 

 change? I'lace near the 1 Ig a crystal of K,A'r._.< > T ; result? De-cribe 

 the phenomena carefully; draw the drop- at intervals showing the 

 nature of the form changes. Xote the resemblance to amoeboid 

 movement, ingestion of bichromate crystals, movement ot drop 

 toward crystal ( anal gy to chemotaxis). 



152. Movements and formation of projections, due to changes 

 in surface tension in a drop of olire oil. a. < hi a slide fasten 

 some glass reds i mm. in diameter, a sufficient distance apart so that 

 they will support a rectangular cover glass near its ends. Make 

 a mixture of two parts glycerine and one part 70' '< alcohol place on 

 the slide, and cover it. Then with a fine capillary pipette introduce 

 :i -mall dm]) of clove oil beneath the cover. Observe that the drop 

 changes its shape and moves about. \\ by J . ( If the drop does not 

 move or moves too violently, vary the experiment by changing 

 the proportion of glycerine and alcohol in the fluid.) 



b. Into Mich a drop of clove oil prepared a- above introduce with 

 a tine capillary a very little 70' < alcohol. clos C to the edge of the 

 drop. Notice the formation of a projection and movement toward 

 this edge. \Vliy? 



c. In the same preparation, or a similar one, touch the upper 

 -iirface "f the cover gla>s near the drop of clove oil with a hot wire. 

 What happens? \Yhy? 



153. I'.lectricallv conditioned chain/es of surface tension. The 

 phenomena of K\p. 151 are at bottom due to electrical change-. I he 

 influence of the current may be shown thu-: Dip wires tr in two 

 OF three dry cell- on the opposite -ide- of a watch-glas- containing 

 a drop of mercury in dilute acid. Result ? Note the direction .>t 

 movement of the drop relatively to the poles, and also ot particles 

 on the surface of the mercury. Make a diagram -bowing this. 



F. SURFACE TENSION I'.KTWKKN SEVERAL SUB- 

 STANCES. 



When a fluid i- in contact with another -ub-iance i -olid, liquid 

 or ga- ) the degree- "l" the -urface ten-inn depend- on both -ub-tances. 



38 



