CHEMISTRY. 493 



percenta/j^e streugth of the solution iu a remarkable mauuer, which they 

 epitomize in the following statement : If the percentages of the salt be 

 expressed by a series of the powers of 2, the chemical action will be ex- 

 pressed by the corresponding powers of 3. In their experiments they 

 employed a plate of copper suspended in a solution of silver nitrate. 

 Since the authors offered no explanation of this law, Professor Langley 

 raised the following questions : Is the rate of metallic precipitation for 

 ^'arying strengths of the solution due to the chemical action alone, or 

 is the operation of chemical affinity compounded with one or more purely 

 physical forces ; and, if so, what is the relative part contributed by each? 



To solve the problem Professor Langley devised apparatus for bring- 

 ing the solution against the plate with uniform velocity ; this was sug- 

 gested by an observation of Gladstone and Tribe that two currents, one 

 ascending and one descending, formed during the precipitation. Pro- 

 fessor Langley arranged a plate of copper so that it revolved 5^- times 

 per second, and as a result of many trials, made iu divers ways, he arrived 

 at this law : In metallic precipitations of dilute solutions the chemical 

 action varies directly as the mass, i. e., percentoge of the dissolved 

 salt. 



Gladstone and Tribe's experimental work was confirmed, and Pro- 

 fessor Langley offers the following explanation of their law : When the 

 plate is suspended in the liquid a film of copper nitrate is at once formed 

 against it. ISTow, the access of fresh silver nitrate de])ends on the re- 

 moval of copper nitrate ; this film, being heavier than the main solutioii, 

 begins to fall (a part also rises), and thus drags in fresh liquid from 

 above to attack the copper. The rate at which it falls depends upon 

 its density, that is, on the quantity of copper dissolved, but it is resisted 

 by the inertia of the surrounding fluid which it must displace. Now, 

 as the percentage of silver nitrate in the solution is increased the den- 

 sity of tbe copi^er nitrate increases, and it will descend faster. The rate 

 of motion, however, is dependent on several considerations, which the 

 author discusses fully, and he concludes that the observed rate of 

 action will be made up of two factors: twice the chemical action 

 because of chemism, and H because of gravitative action ; or, when the 

 percentage of silver salt is doubled, the quantity of copper dissolved 

 will be tripled. This is Gladstone and Tribe's law. 



The author thinks it probable that the true law of chemical action, 

 where one metal precipitates another, should be that the time during 

 which one atom replaces another in a compound molecule is constant, 

 and hence that the rate of total chemical action varies directly as the 

 mass of the reacting body in solution. {Journ. Chem. ISoc, December, 

 1884.) 



Certain Phenomena attending Mixture, by Prof. F. Guthrie.— Experi- 

 ments conducted with a number of different liquids show that mixtures 

 can be arranged in two distinct classes. Of the first a mixture of 

 water and ether is an example ; wdien shaken up together they mix, heat 



