pentol and benzol here employed had the specific gravities of 0.863 and 0.864 respectively; they may therefore be considered of equal density. Hence variation in the liquid medium, independent of variation in its deusity, produces an enormous effect upon drop-size. We shall have occasion to return to this case. The influence which the liquid medium exerts on the drop-size, and the share of that influence due to the specific gravity of the medium, will be well seen on comparing the drop-sizes of mercury which falls through various liquid media. The arrangement of the apparatus for this purpose is seen in Plate V. fig. 8. As far as A it is similar to fig. 7. The siphon A, fig. 8, is a capillary tube; its lower end, which is turned vertically downwards, rests upon a sphere of brass, R, which has been washed with nitric acid and sodium-amalgam, and allowed to soak for some days under mercury. Mercury adheres perfectly to such a sphere. In every case the sphere was immersed just halfway in the liquid. A small capsule S is supported in the liquid on a stand T about half an inch lower than the bottom of the sphere. As soon as gt becomes constantly 5", the vessel V is moved so that S comes under R. Five drops of mercury having been caught, the cup is moved horizontally as before, taken out and replaced by a fresh one, and so on. The batches of five drops are washed, dried, and weighed. The results are given in Table XV. We may, however, previously notice here with advantage a phenomenon which attends the separation of drops under several circumstances, but which can be watched most narrowly in the cases of SLL, because in a liquid the separation of a drop is less abrupt than in a gas. When water falls from glass through air, immediately after the drop separates, a very minute drop is frequently projected upwards from the upper surface of the drop*. I have not traced the conditions under which this supplementary drop is formed; indeed it is sometimes formed, and sometimes not, under apparently similar circumstances. No doubt the proximate cause is that the drop at the instant of separation is not spherical; the persistent or retentive cohesion, which brings it almost immediately to its normal shape, does not allow time for its more excentric parts to collect to the main mass; they are therefore by the motion of the main drop flung off and projected upwards. The same phenomenon is seen much more distinctly when water drops at this rate (gt=5") through benzol or turpentol. In these cases the persistent cohesion of the liquid medium comes also into play. But the most striking example of supplementary drops is seen when * The secondary drop may be well shown by holding a plate containing anhydrous cupric sulphate about two inches below the dropping solid. The white salt is smoothened by pressure under a plate, and its surface, being porous, absorbs the water-drops instantly and without splashing. The blue spots of hydrated sulphate show where the water has fallen. |