371 ^ 



The usefulness of the metliod is sufficiently demonstrated by these 

 experiments. Moreover they can easil}' be so arranged, that the 

 surface tension is determined in vacuo, in which case |)robahly a 

 gradual change of o with the time would not show itself^). 



§ 7. Instead of forming the mercury drop on the top of a capillary 

 it is possible to make it form at the bottom. This can be done by 

 closing a wide tube at the bottom l)y a plate with a small circular 

 hole; mercury being poured in, a small hanging drop is formed at 

 the orifice, which gives way at a definite maximum height of the 

 mercury in the tube, after which the meicury runs out. From the 

 observed maximum height and the radius of the opening the surface 

 tension of the mercury niay be derived. 



If H represents the height of the liquid in the wide tube above 

 the opening, H = h' — y, li' being the height of the mercury in the 

 wide tube above the bottom of the hanging drop and y again 

 representing the height of the drop. In this case k is negative (see 



2 

 Suppl. N'. 42c), hence k — — = — h' and H = — {h -\- y). The 



condition for the maximum of H at constant .i' = ?■ then leads to 



the same equations as in § 5, except that k and H have to receive 



the negative sign. 



It follows in the first i)lace that a>, (eq. 9) is negative; that 



jr 

 is: the drop begins tu fall before 'p has reached the value — (see 



§ 3), so that h in this case cannot reach its maximum value 

 (§ 4). In the second place according to eq. (11), H^ being reckoned 

 as positive, 



o-=r|(ft~,,J.//y,„r(^l+|^^-i£^j . . . (11') 



§ 8. By tliis method also a determination was made of o for 

 mercury, F'or this purpose a tube of 1.5 cm i-adius was closed at 

 the bottom by a plate, through a hole of which a short piece of 

 glass capillary (?*:= 0.522 mm) had been stuck. When mercury was 

 put into the tube a drop at a time, a drop was formed at the 

 lower end of the capillary which gave way before the hemisphere 

 had been reached. 



Here again the value of H,n was very strongly dependent on the 

 time elapsing while the drop was being formed; the greatest value 



1) In a vacuum Fürth (Wien. Sitz. Ber. |2a), 1:26 (1917) p. 329) found t — 440 

 to 445 at 18-G; in this no trace of a change of <t with the lime was observed. 



