WITHDRAWN FROM THE ACTION OF GRAVITY. 627 



dense portions descend to the lower part, and tend to depress it. 

 Now the quantities of pure alcohol, and 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 undoubtedly not equally 

 exerted upon the two principles of which the oil is composed. 

 Hence before taking the measures, the different parts of the oil 

 must be intimately mixed together, which may be effected by 

 introducing an iron spatula into the mass, moving it about in it 

 in all directions, and this for a long time, because the mixture 

 of the oil can only be perfectly effected with great difficulty on 

 account of its viscidity. 



To avoid the influence of the reactions which render the oil 

 heterogeneous, the operations must be conducted in the follow- 

 ing 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 alcoholic 

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

 the equilibrium of the densities altered by the chemical reac- 

 tions and the variations of temperature. 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, w-hich is to be carefully corked; withdraw with the 

 syringe the small poi'tion 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 following is the reason why the oil must be removed from the vessel 

 before employing it for the experiment. After having remained a considerable 

 time in the alcoholic liquid, the oH becomes enveloped by a kind of thin pel- 

 licle ; or, more strictly speaking, the superficial 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 



