Mercury -still for the Rapid Distillation of Mercury. 501 



Solvent. ! Dissolved substance. 



! 



Molec. depression. 



Increase. 



100 H o 1 to 7 CaOl, 

 100 (GaCl.,6H.,0) 1 to 800 H 2 

 100 H 2 • . 1 to 13 C,H 6 



2°773 to 6-9 

 0003 to 0099 

 1-11 to 118 



150 per cent. 

 3200 

 6 



The increase in the case of alcohol is small, but still there 

 is an increase, and not a decrease ; while in the case of water 

 in the hydrate of calcium chloride the increase is almost the 

 greatest at present known. 



Irregularity of the Deviations ivith Weak Solutions. 



That the deviations from constancy are not regular, and are 

 not even always in the same direction, will be seen on referring 

 to the results with sulphuric acid dissolved in water (p. 499) ;, 

 the depression in the freezing-point of the tetrahydrate, both 

 by water and sulphuric acid, supplying two other instances of 

 a similar character. 



Since every fact which can be used to test whether the theory 

 of osmotic pressure is a true explanation of the nature and 

 behaviour of solutions, either fails to give any evidence in its 

 favour, or else gives evidence directly opposed to it — evidence, 

 often, of the strongest possible character — this theory can 

 certainly not yet be regarded as established. 



LVII. A Mercury-still for the Rapid Distillation of Mercury 

 in a Vacuum. By Frederick J. Smith, M.A., Millard 

 Lecturer in Mechanics and Physics, Trinity College, Oxford* '. 



WHEN mercury is distilled in a vacuum, in the usual 

 apparatus, a large portion of it when vaporized, on 

 reaching the internal domed surface of the bulb in which the 

 operation is conducted, forms itself into minute spheres, which 

 grow heavy and run down the inside of the bulb ; and only a 

 small quantity of the metal finds its way into the central tube, 

 from which it is caught for use. 



The advantage of the new form of vacuum mercury-still, of 

 which I venture to give an account, is that all the mercury, 

 which condenses in the head of the bulb, is prevented by its 

 shape from returning to the mercury from which it has been 

 separated by heat. This is not the case in the mercury-still 

 of Weinhold, or Clark, or in those stills in which only the 

 mercury which collects in the eduction-tube is caught, as in 

 * Communicated by the Author. 



Phil. Mag. S. 5. Vol. 29. No. 181. June 1890. 2 Q 



