210 THE FIGURES OF EQUILIBRIUM OF A LIQUID MASS 



the liquor, forms a globule, to wliicli a diameter of about two centimetres* must 

 be given, and which a little shake will detach from the mouth of the funnel if 

 it does not detach itself. Then, accordingly as this globule falls to the bottom 

 of till- liquor or rises to its surface, wc conclude that the quantity of alcohol of 

 the mixture is too great or too small ; we therefore add to this a little water or 

 alcuhol, taking care to stir it well, and recommence the experiment of the test 

 tube, 'i'he same operations are repeated until the globule of oil remains sus- 

 penii'd in the liquor, without appearing to have a tendency either to fall or rise. 

 The mixture may then be considered as approaching very nearly the desired 

 point. 1 say very nearly, for the globule of oil of the test tube, being of small 

 dimensions, has more dilHculty in moving in the liquor than spheres of a large 

 diameter, and it may seem to be in equilibrium of density with the surrounding 

 liquid, whilst for a larger volume of oil this equilibrium does not exist. 



4. Wht-n the alcoholfc mixture, which I presuppose to be contained in a 

 lar"-e glass llask of the ordinary form, has attained this point of approximation, 

 the next thing is to introduce the mass of oil. For this purpose the long-necked 

 funnel which has been mentioned above must be again used, and this must 

 reach to a certain depth in the liqiior contained in the flask. Letting the funnel 

 rest on the neck of the latter, we pour the oil slowly. Then, if the alc.oholic 

 mixture is by chance exactly in the requisite proportions, the oil forms, at the 

 extremity of the neck of the funnel, a sphere, the volume of which increases 

 gradually in proportion as we add this last liquid. When the sphere has at- 

 tained the volume we desire, the neck of the funnel is withdrawn with caution; 

 the sphere which adheres to it rises with it toward the surface of the liquor, 

 and the oil which it still contains is added to the preceding. Lastly, when the 

 sphere has nearly reached the surface of the alcoholic mixture, a little shake 

 detaches it fiom the funnel. Ordinarily, however, the mixture has not so exactly 

 the desired density. We then see, in general, several successive spheres of oil 

 formed, which, detaching themselves one after another from the mouth of the 

 funnel, fall slowly to the bottom of the flask, or rise to the surface of the alco- 

 liolic liquor. Li this case all these spheres should, in the first place, be united 

 into one, Avhich is easily done by the following means. We introduce into one, 

 of them the end of an iron wire. The adherence which the oil contracts with 

 'this metal then allows the sphere in question to be easily conducted in the am- 

 bient liquid, and to be led to join with a second sphere, t By continuing this 

 treatment, we soon succeed in uniting all. Then, according as the whole sphere 

 shall remain at the bottom or on the surface of the liquor, add cautiously to the 

 latter a certain quantity of water or of alcohol ; and, after having corked the 

 flask, we next turn it several times slowly, and so as not to disunite the sphere 

 of oil, until the mixture is well effected, Avhich will take place when we no 

 longer perceive any striae in the liquor on looking through it at a window. 

 Lastly, the same operation is to be repeated until the sphere of oil is perfectly 

 in equilibrium in the surrounding liquor. 



5. If the experiment has been made, as I have supposed, in a flask of the 

 ordinary form, that is to say cylindrical, the mass of oil does not, however, ap- 

 pear exactly spherical; it is widened in the horizontal direction. But this is 

 only an optical illusion, attributable to the form of the flask. The latter, with 

 the liquor whieh it contains, acts in the manner of a cylindrical lens whose axis 



* S(^ table of measures at the end of this vohime. 



t III order tlms to compel two sphcros to unite, it does not snfiBce to put them in contact 

 with one another. They niig^ht touch for a lonfj time without mingling into one; one would 

 say that they are enveloped in a resistinfj pellicule which opposes their union. It is also 

 necessary, tlierelbre, to introduce the extremity of the metallic wire into the second sphere, as 

 if we wished to break the partition which separates the two masses. The union is then cflocted 

 immediately. I'shall revert to these phenomena hereafter. 



