Chemistry and Physios, 391 



what higher than the mercury level in the measuring tube, and 



the pressure tul»e is raised until the mereury in the reduction 

 tube exactly reaches the 100 mark. If now the measuring tube 

 be raised until the mereury within it is at exactly the same level 

 a- that in the reduction tube, it is evident that the gas it contains 

 Occupies the volume which it would have at 0° and under 7«;o mm 

 pressure, since this is the condition of the air in the reduction 

 tube which communicates with it. Hence the corrected volume 

 can be read off at once on the measuring tube. Various modifica- 

 tions of the form of the apparatus for special cases are described. 

 — Ber. Berl Chem. Ges., rxiii, 440, March, 1890. ... v. b. 



j. Onthi Nature of Solutions. — Pickering has published an 

 extended paper on the nature of solutions, as elucidated by a 

 study of the density, electric conductivity, heat-capacity, heat of 

 dissolution and expansion by heat of sulphuric acid solutions, 

 following the suggestion of Mendeleeff that by plotting the rate 

 of change, i. e., the first differential coefficient of the density, con- 

 ductivity, etc., of the solution as a function of the percentage 

 composition, any sudden alterations in the curvature might be 

 more satisfactorily established. But the statement of Mendeleeff 

 that the derivative yielded a straight line or a series of straight 

 lines, was found to be true not of the first but only of the second 

 derivative. The curves for example which represent the first 

 differential coefficient of the densities of sulphuric acid solutions, 

 though continuous, are made up of a series of separate curves 

 which on further differentiation yield a series of straight lines. 

 So if the contractions obtained on mixing sulphuric acid and 

 water be plotted instead of the densities, while a curve totally 

 unlike that of the densities is obtained, yielding a first derivative 

 curve also unlike that of the densities, the second derivative 

 yields a right line closely resembling the second derivative of 

 the densities and indicating the existence of changes at the same 

 points. In the same way the electric conductivities, heat-capaci- 

 ties, heats of dilution, and expansions are represented by curves 

 which split up by two differentiations into a series of straight 

 lines, showing changes at the same points. These points corre- 

 spond to simple and definite hydrates of sulphuric acid amounting 

 to as many as 17, the mono-hydrate being at one extreme and a 

 hydrate with 5,000 H 2 being at the other. "The main facts 

 elucidated by this work," the author says, " afford absolute proof 

 that the properties of solutions do not vary regularly with their 

 composition, and that the nature of the solution is therefore not 

 merely physical. There can be no doubt but that solutions con- 

 sist of hydrates of a definite composition, though these may 

 always be in a state of partial dissociation." — J. Chem. Soc, lvii, 

 64, March, 1890. G. f. b. 



3. On the Density of Fluorine. — By using a larger apparatus in 

 the preparation of fluorine by electrolysis and by purifying the gas 

 from hydrogen fluoride by passing it first through a platinum worm 

 cooled to —50° by means of methyl chloride and then through a 



