on the whole, the sizes of the drops at the slower rates are less influenced by equal increments of gt than are those of the quicker rates. This, however, only appears distinctly at and below the rate of about gt=1"-00.

If the connexion between gt and the drop-size be represented by a curve (fig. 2, A), the abscissæ being the values of gt, and the ordinates the corresponding drop-weights, there is apparently no asymptote parallel to I the axis of X. The curve presents, however, in its course two secondary maxima and minima:

Although at these minima the drops are less than at the immediately succeeding rates, yet the quantity of liquid passed in a given time is, at every rate of dropping, greater than the quantity passed in the same time at every slower rate. The decrease of rate more than counterbalances the temporary increase in the drop-size. This is seen on comparing the numbers of column 3, Table IV., with one another. They are found to decrease continually, though by no means uniformly, as the rate of dropping decreases. The same fact is shown graphically in fig. 2, B.

The second maximum (at gt =·500 and gt='517) is in remarkable connexion with the rate at which a series of drops may be converted into a continuous stream. At all rates of dropping, from gt=333 to gt='517 inclusive, the drops may be converted into a permanent stream by pouring a little additional oil upon the sphere as the drops are falling from it. A stream is thus established which remains for any length of time, if it be protected from all currents of air and vibration. At the rate gt=519 the stream may be established by the same means for a few seconds (about 30"), but the continuous part inevitably begins to palpitate, becoming alternately longer and shorter, thinner and thicker, until at last it draws up and is converted into a succession of drops. At the immediately slower rates of dropping the same effect follows, but in each case in a shorter time, so that the slowest rate of dropping, which may be converted into permanent running, coincides with the rate which gives the second maximum size of drops (gt=500 and gt=517). The appearance of a dropconvertible stream is peculiar, the narrowing which it undergoes on leaving the solid being remarkably sudden.

In many liquids such secondary maxima are entirely wanting. They appear in liquids of the physical nature of oils, whether those oils be chemically fatty (adipic salt of glycerine), or whether they be miscible with water, as syrups, glycerine itself, &c.

In order to avoid the influence of variations in rate, we shall for the future take the same rate of dropping in all cases, and, unless the contrary be stated, the rate adopted will be gt=2".

The factor, the influence of whose variation on the size of the drop we have next to consider, is the constitution of the liquid of which the drop is formed. For the foregoing experiments concerning the influence of rate, cocoa-nut oil was employed on account of its non-volatility. On allowing a quantity of it, having an exposed surface of about two square inches, to stand for 70 hours, it was found to have increased about 2 milligrammes in weight, probably in consequence of oxidation. Its fixedness, therefore, and its perfect liquidness at the temperature of 28°-30° C., make it well adapted for this special purpose. Chemically and physically, however, it is of little interest for our immediate purpose, because it is a mixture of several substances, the proportion between which is indefinite.

be a

The constitution of a liquid may vary in two ways. A liquid may mixture of two or more simple liquids, or a solution of one or more solids in a single or mixed liquid; or secondly, the liquid being single, may vary in the sense of its chemical constitution. It would be clearly impossible to exhaust experimentally the countless variations which might thus arise. We must be satisfied with taking a few simple examples of the two

I cases.

With the more mobile liquids the apparatus, fig. 1, fails to give a strictly uniform flow. As the liquid descends in B, it adheres by capillary action to the lip of A for some time after the level of B is below the lip. The air at last separates the two, enters the flask A, displaces the liquid there, and restores the level to B, so that although the average height of B is constant, yet it undergoes a series of slight but ceaseless variations. As even such slight irregularities sensibly affect the rate of flow through the siphon, and consequently the rate of dropping from the sphere, the apparatus is slightly modified as follows, fig. 3. Between the reservoir, B, fig. 1, and the dripping sphere, a second reservoir, M, is placed. This is kept in a state of continual overflow. The overflow is regulated by means of a few filaments of cotton wool hanging over the edge of the overflowing vessel, and so fashioned that the end in the overflowing vessel tapers to a point. Finally, the rate of flow is in many instances so sensitive, that it is impossible to procure exactly a predetermined rate by the ordinary screw-adjustment of the holder which carries the siphon. For the final adjustment, it is convenient to depend upon the elasticity of the siphon. A heavy ring is passed over the siphon, which is then firmly fixed so as to deliver the liquid at nearly the required rate. The ring slipped backwards and forwards, bends the siphon more or less, and regulates the flow through it.

Solution of Chloride of Calcium in water.-A solution of chloride of calcium, nearly saturated at 28° C., was taken as the starting-point or solution of maximum saline contents. Half of this solution was mixed with an equal volume of water (solution 2). Half of solution 2 was mixed with its own volume of water, giving solution 3, and so on. In this manner, without knowing the absolute strength of solution 1, we know

that the successive strengths of the saline solutions, whether there be loss co

of volume owing to chemical union or not, are as 8,

8 8 8

2' 4' 8'

0.

dr

These numbers give exactly the relative quantity of solid matter in a unit of volume of the liquid. As, however, solution 1 on dilution evolves heat and therefore probably contracts, the sizes of the drops cannot be derived directly from their weights. The specific gravity of each solution has to be determined experimentally.

The column of the relative sizes of the single drops (which is got by dividing the mean weights by the corresponding specific gravities) shows that, under like conditions, a drop of water is larger than a drop of solution of chloride of calcium of any strength whatever. The comparatively small quantity of solid matter in causes the drop to diminish about 4th of its

volume.

8 128

We must bear in mind that the successive increments of solid matter may affect the size of the drop in opposite directions,-by affecting the

* The first number from six, the following numbers from four determinations of the weight of 30 drops.

cohesion of the water, by asserting its own cohesion, by increasing the gravity of the liquid and thereby determining an earlier separation of the drop, and, in this particular case, by the chemical affinity of the solid to the liquid, and the probable formation of hydrates. It is seen that these influences cause an irregularity in the diminution of the size of the drop as it acquires more solid matter. In fact, it is only when the liquid has

8

the considerable strength of that the diminution in drop-size becomes

continuous.

8

In fig. 2, C shows graphically the relation between drop-size and strength. The abscissæ represent the strengths of the solution progressing in geometric

ratio; the ordinates show the corresponding comparative drop-sizes. It may be remarked that the curve C bears a striking resemblance to the curve A, as though increase in solid constituent produced a similar effect upon the drop-size as increase in the time-interval on the drops of a homogeneous liquid. We may also notice the great difference in size between a drop of water and a drop of oil under the same conditions. From Table IV. we find that a drop of oil of specific gravity 9195 has the weight 05986 when gt=2". Hence the comparative sizes of the two are,

Or a drop of water is nearly three times as large as the drop of oil, the only difference in the circumstances being that the oil was 10-104 C. warmer. We shall have to study this point more especially hereafter.

On account of the chemical union which takes place on dissolving Ca Cl in water, it would be useless to give the absolute strengths of the various solutions.

VOL. XIII.

2 L

Solution of Nitrate of Potash in water.-Nitrate of potash was the ner solid examined, on account of the probable non-existence of hydrates. Seven solutions of nitrate of potash were made of the following strengths by weight:

(1) 22 of water to 1 of nitrate of potash.

These solutions were made to drop from the ivory sphere at the rate of gt=2". In each instance four batches of drops, of 30 each, were weighed. In the following Table the mean results only are given.

Hence it appears that on the addition of the first quantities of nitre

(22, 22, 22, 22) the size of the drop is diminished. Afterwards

(22, 22, 22)

I

う