1864.] Prof. Guthrie on Drops. 453 



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 hoars, it was found to have increased about 2 milli- 

 grammes 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, how- 

 ever, it is of little interest for our immediate purpose, because it is a mix- 

 ture of several substances, the proportion between which is indefinite. 



The constitution of a liquid may vary in two ways. A liquid may be a 

 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 

 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 irregulariti'es sensibly afi'ect 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 back- 

 wards and forwards, bends the siphon more or less, and regulates the flow 

 through it. 



Solution of Chloride of Calcium in wafer. — 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 



