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drawn with centre H, we have the sectional view of the optical convex mirror which will give the same position of image as the magnetic convex mirror shown by the circle CED.
In conclusion, it may be remarked that the construction of fig. 14 affords a new and simple graphic method of finding the position of optical images, by the device of using the auxiliary circle whose diameter is the radius of the spherical surface.
XXI. Notices respecting New Books.
The Scientific Basis of Analytical Chemistry. Die wissenschaftlichen Grundlagen der Analytischen Chemie. Ele
mentar dargestellt von W. OSTWALD. (Leipzig: Wilhelm
Engelmann. 1894.) IT has been so long the custom with a certain class of teachers in
this country to regard analytical chemistry as synonymous with chemical science that the very title of this book will come as a surprise. Prof. Ostwald, in the present little volume of 187 pages, has attempted to present the subject of chemical analysis in a popular form and in a new way. Whether he has succeeded in his objects in his own country it is difficult to say, but so far as English chemists are concerned the book is certainly not likely to achieve popularity: first, because it is not arranged in accordance with our examinational notions of chemical analysis; and, secondly, because it bases the analytical properties of the elements and their compounds on a theory which has not found general acceptance in this country, viz. the theory of ionic dissociation. But in calling attention to these two points we are really bestowing praise upon the work; because any novelty of treatment in such a well-worn field is to be cordially welcomed, and all attempts to approach the subject from a different scientific aspect to that generally adopted are bound to help in the “ depolarization” of cut and dried dogmas which are so baneful to true progress in science.
Of the two parts into which the book is divided, the first, consisting of five chapters, deals with theory, and the second, consisting of eight chapters, deals with applications. The theoretical part, where concerned with the ordinary operations, is lucidly put together, and forms quite pleasant reading as compared with the purely cookery-book kind of directions that the student in this country is expected to follow. We doubt much whether the average “ certificated teacher” knows that there is any scientific theory behind the processes which he has been drilled into carrying out. It is in the fourth chapter, under the heading Die chemische Scheidung, that the new theory of solutions is first broached, and from that part onwards everything connected with the subject is treated of from the point of view of ionic dissociation. Whether this view is accepted or not, it must be conceded that Prof. Ostwald
Phil. Mag. S. 5. Vol. 39. No. 237. Feb. 1895. Q
has made out a good case in support of its applicability to the ordinary processes of analysis. The key-note is struck on p. 47 in the following extract, which we paraphrase :
“In aqueous solutions of electrolytes the ions are generally partly combined and partly uncombined. In neutral salts the uncombined portion is by far the greater, and is in fact the more in preponderance the more dilute the solution. The properties of dilute salt-solutions are consequently determined, not so much by the properties of the dissolved salt as such or by the combined ions, but rather by the properties of its free ions. Through this co:ception the analytical chemistry of saline matter (salzartigen Stoffe) at once undergoes an enormous simplification : it is not the analytical properties of salts as a whole, but only those of their ions which have to be established. Supposing that 50 anions and 50 kations are viven, these can form with each other 2500 salts ; and supposing these salts to possess individual reactions, the properties of 2500 kinds of matter must be individually enunciated. But since the properties of the dissolved salts are simply the sums of the properties of their ions, it follows that the knowledge of 50+50=100 cases is sufficient to predominate over the whole possible number of 2500 cases. As a matter of fact, analytical chemistry has long made use of this simplification. It has long been known, for example, that the reactions of the copper salts are the same with respect to copper, whether we examine the sulphate, nitrate, or any other salt; the scientific formulation and the cause of this behaviour have, however, been reserved for the dissociation theory.”
Any polemically disposed chemist might feel inclined to traverse the last statement, but we have said enough to show that we have at any rate a work on chemical analysis which can in reality be called a new work. It is worthy of the most careful study, and its pages will be found interesting both by veterans and novices ; an opinion which is tantamount to the highest praise that can be bestowed upon a book devoted to a subject in which there has been practically no scope for a new departure since the time of Liebig.
XXII. Intelligence and Miscellaneous Articles.
ON THE CHANGE OF LENGTH IN SOFT IRON WIRE PLACED IN A
UNIFORM MAGNETIC FIELD. BY B. ROSING.
To the Editors of the Philosophical Magazine. GENTLEMEN, IN N No. 224 (vol. xxxvii.) of your esteemed Magazine was pub
lished a paper by Mr. Nagaoka on “Hysteresis attending the Change of Length by Magnetization in Nickel and Iron." Since the autumn of 1891 I have been investigating the same question,
ī X 10.
and the results I have now obtained agree in general with those of Mr. Nagaoka. Some discrepancy between our observations may be explained as due to a divergence in the conditions of experiment*. The method I used consisted in the application of interference-fringes and sensitive lever. Its sensitiveness was nearly the same as that in the method of Mr. Nagaoka: one division of the microscope scale corresponding to a change of length
=11x 10-7 cm. Influence of temperature effects was compensated by a peculiar bimetallic suspension of the sensitive lever. The results I have obtained are given in the following Table,
ol where H represents magnetic force (C.G.S. units), elongation per unit of length of my iron wire t, and I its magnetization.
+ 13.6 + 24:3 + 29 5 + 29.5 + 26-6
Theoretical views permit us to suppose the following correlation
δι between and corresponding values of H and I – 7 87
(1) =al? +BIH+CH? ī
My friend Mr. Weinberg has kindly calculated the coefficients of this formula by the method of least squares.
These are as follows:
a=4.4834 x 10-14, b=-365.023x10-14, c=3015•31 x 10-14.
The iron bars of Mr. Nagaoka were comparatively thick and short, the ratio of their length to their diameter was not greater than 70, whereas my wire bad for this ratio about 494. This wire was moreover stretched.
† Mean of several sets of observations.
The dotted curve on the accompanying figure represents the
öl relation between and H calculated by the formula (1), and the
1 plain curve the results of observations.
cl The mean difference between the values of
observed and calculated is equal to about 6.7 x 10-9 or to 3 per cent. of the maximum value. This difference is too great for an exact formula, but as a first approximation the formula (1) may be accepted. Thus I may set forth the results of iny investigation in the following form :A soft iron wire, 39.5 cm. long and 0:083 cm. thick, with a longi
gr. tudinal stress of 380 and placed in a magnetizing solenoid 86 cm. long and 3.85 cm.” in mean section, by cyclic magnetization show's a change of length, which may be expressed, as a first approximation, by the formula
0.000044834 x 1?- 0·00365023 x III +0·0301531 x H',
is elongation per unit of length, I magnetization, and H magnetic force.—Abstract of a paper published in the Journal of the Russian Physico-Chemical Society, xxvi. pp. 253-264.
Physical Laboratory, University of St. Petersburg, Russia.
LONDON, EDINBURGH, AND DUBLIN
JOURNAL OF SCIENCE.
XXIII. Some Experiments with Alternating Currents. By
ALBERT GRIFFITHS, M.Sc., Berkeley Fellow of Owens
College, Manchester*. THIS paper embraces experiments on certain actions proj the coil or coils of a galvanometer, and investigations of a peculiarity noticed by Lenard, viz., that the resistance of bismuth in a strong magnetic field, when measured with an alternating current and a telephone, is greater than when measured with a steady current and a galvanometer; in addition there are some theoretical considerations.
As mentioned by Dr. Schuster in Phil. Mag. vol. xlviii. 1874, p. 340, it is found that if an alternating current and constant current combined go through the coils of a galvanometer, the deflexion of the needle is greater than that produced by the constant current alone.
In my experiments, an induction-coil supplied with Kohlrausch's apparatus for the determination of electrolytic resistance was used as the source of the alternating current, the interrupter of which was replaced, initially, by a tuningfork which gave 128 complete vibrations per second.
The galvanometer employed was one of Edelmann's : there is a pair of coils on each side of the needle which can be
* Communicated by Prof. A. Schuster, F.R.S. Phil. Mag. S. 5. Vol. 39. No. 238. March 1895. R