428 



THE FIGURES OF EQUILIBRIUM OF A LIQUID MASS 



first sought to verify for bubbles of glyceric liquid of very different diameters. 

 Fig. 8 The apparatus of which I made use is 

 represented at Fig. 8, in vertical pro- 

 jection ; G ^ is the upper part of a sup- 

 port, whose total height is 40 centime- 

 tres. On this support is fixed a tube 

 of copper, c d f,to the extremity c of 

 which is fixed with mastic a bent tube 

 of glass, c g hk, designed to serve as a 

 manometer, the interior diameter of 

 which is about one centimetre; the 

 length, d g, is 20 centimetres. The 

 copper tube has, at /, a horizontd 

 branch, which it was not possible to 

 represent in the same figure, because 

 it is directed towards the spectator, 

 but which is seen apart at I m, (Fig. 9.) 

 To the extremity m is centented a glass tube, m n, whose in- 

 terior diameter is but about 2 millimetres. Lastly, at the ex- ^^S- 9 



tremity y of the copper tube (Fig. 8) is soldered an adjutage ^^ 

 of iron, f j)' widened below into a small funnel, whose border 

 has a diameter of 5 millimetres ; this funnel has been slightly 

 oxidized by diluted nitric acid, (§ 14.) 



To use this apparatus, we commence by introducing dis- 

 tilled water into the manometer g h k m sufficient quantity to 

 occupy a height of some centimetres in the two branches ; we 

 then convey under the adjutage f j^ ^ capsule containing the 

 liquid destined to form the bubbles; we plunge therein the 

 border j) of the small funnel, and lower the capsule; then, applying the mouth 

 to the orifice n of the glass tube of the branch, (Fig. 9,) we blow with caution. 

 A bubble quickly appears at the adjutage, to which, with the precautions to be 

 presently indicated, is given such a diameter as may be deemed suitable, and 

 when this is obtained, the orifice n is carefully closed with a small ball of wax. 

 The water is now rather higher in the branch h k of the manometer (Fig. 8) than 

 in the branch Jig, on account of the pressure exerted by the bubble, and it only 

 remains to measure the difference of the above level and the diameter of the 

 bubble. For the first of these measurements, we avail ourselves of the cathe- 

 tometer in the usual manner, and, for the second, we lay the same instrument in 

 a horizontal position upon suitable supports. 



§ 27. These experiments, though very simple in principle, present consid- 

 erable difficulty in the execution. In the first place, the air which we breathe 

 into the ajiparatus is warmer than the ambient air, so that the bubble, after its 

 formation, becomes a little contracted by reason of the gradual cooling of the 

 air contained within it and in the tubes of the instrument ; whence it is neces- 

 sary to wait some time before proceeding to measure the diameter. In the 

 second place, bubbles of great diameter exerting but very feeble pressure, a 

 small error in the measure of the latter has a considerable influence on the pro- 

 duct ^(i/ it is therefore requisite, in order that the results may not oscillate too 

 greatly around the true value, to stop at a certain limit of the diameter. In the 

 third place, very small bubbles have also their inconveniences ; to bring them to 

 the desired diameter, and to obviate, at the same time, the contraction by cool- 

 ing, they are at first inflated much beyond the size they are intended ultimately 

 to have, and are then left to diminish spontaneously by the expulsion of a part 

 of the air which they contain; now, when this diminution has reached a certain 

 point, it becomes very rapid, and much address is required to apply the ball of 

 wax at the exactly proper moment Moreover, these small 'bubbles seem to have 



