254 THE FIGURES OF EQUILIBRIUM OF A LIQUID MASS 



the quantities of pure alcohol, aucl that at 16° added to the alcoholic mixture 

 • to balance the mass, necessarily produce an alteration in the homogeneity of 

 the oil ; for, in the first place, the oil during these operations being in contact 

 with mixtures which are sometimes more, sometimes less charged with alcohol, 

 must absorb or lose some of this by its surface; in the second place, these same 

 additions of alcohol to the mixture diminish the saturation of the latter with 

 the oil, so that it removes some of it from the mass; and this action is undoubt- 

 edly not equally exerted upon the two principles of which the oil is composed. 

 Uence, before taking the measures, the different parts of the oil must be inti- 

 mately mixed together, which may be effected by introducing an iron spatula 

 iuto the mass, moving it about in it in all directioift, and this for a long time, 

 because the mixture of the oil can only be perfectly effected with great diffi- 

 culty on account of its viscidity. 



To avoid the influence of the reactions which render the oil heterogeneous, 

 the operations must be conducted in the following manner : The mass being 

 introduced into the vessel and attached to the two rings, and the equality of 

 the densities being perfectly established, allow the mass to remain in the alco- 

 holic liquid for two or three days, re-establishing from time to time the equi- 

 librium of the densities altered by the chemical reactions and the variations of 

 temijerature. Afterwards remove the two rings from the vessel, so that the 

 mass remains free; remove almost the whole of this, by means of a siphon, into 

 a bottle, which is to be carefully corked ; withdraw with the syringe the small 

 portion of oil which is left in the vessel, and reject this portion. Next replace 

 the two rings, and mix the alcoholic liquid perfectly ; then again introduce the 

 oil into the vessel, taking the precaution of enveloping the bottle containing it 

 with a cloth several times folded, so that the temperature may not be sensibly 

 altered by the heat of the hand.* Then attach the mass to the lower ring only, 

 the upper ring being raised as much as possible ; mix the oil intimately, as we 

 have said above ; then de^jress the upper ring, cause the mass to adhere to it, 

 elevate it so as to form an exact cylinder, and proceed immediately to the 

 measurement. 



* The followiug is the reason why the oil must be removed from the vessel before employ- 

 ing it for the experiment. After having remained a considerable time in the alcoholic liquid, 

 the oil becomes enveloped by a kind of thin pellicle ; or, more strictly speaking, the super- 

 ficial layer of the mass has lost part of its liquidity, an effect which undoubtedly arises from 

 the unequal action of the alcohol, upon the principles of which the oil is composed. The 

 necessary result of this is, that the mass loses at the same time part of its tendency to assume 

 a determinate figure of equilibrium, which tendency must, therefore, be completely restored 

 to it. This is why the oil is withdrawn by the siphon. In fact, the pellicle docs not pene- 

 trate the interior of the latter, and during its contraction continues to envelop the small por- 

 tion remaining; so that after the latter has been removed by the syringe, which ultimately 

 absorbs the pellicle itself, we get completely rid of the latter. 



Before using the siphon, the thickness and consistence of the pellicle are too slight to 

 enable us distinctly to perceive its presence; but when the operation of the siphon is nearly 

 terminated, and the mass is thus considerably reduced, we find that the surface of the latter 

 forms folds, hence implying the existence of an envelope. Moreover, when the siphon is 

 removed, the small residuary mass, which then remains freely suspended in the alcoholic 

 liquid, no longer assumes a spherical form, but retains an irregular aspect, appearing to 

 have no tendency to assume any regular form. 



This indifference to assume figures of cqtiilibrium, arising from a diminution in the 

 liciuidity of the superficial layer, constitutes a new and curious proof of the fundamental 

 ])rinciplc relating to this layer, (H (i I/is and 10 to JG.) M. Ilageu {Mcmoirc sur la Surface 

 tics Liquidcs, in the Memoirs of the Academy of Berlin, ]84r>) has observed a remarkable 

 fact, to which the jjrecediug appears to be related. It consists in this, that the surface of 

 water, left to itself lor some time, undergoes a peculiar modification, in consequence of which 

 the water then rises in capillary S|nices to elevations which are very distinctly less than is 

 the case when its surliice is exeinpt or freed from this alteration. This fact might, perhaps, ' 

 be explained Ijy admitting that tlw water dissolves a small proportion of the substance of the 

 solid witii which it is in contact, and that the external air acts cliemically at the surface of 

 the liquitl upon the substance dissolved, thus giving rise to the formation of a slight pellicle 

 which modilies the eflects of the molecular forces. 



