92 



NATURE 



[May 28, 1891 



Contributions to mineralogy, No. 51, by F. A. Genth. A 

 new species, which has been named aguilarite, is described. It 

 appears to be a cupriferous stephanite with an admixture of 

 metallic silver. — Colurnbite of the Black Hills, South Dakota, 

 by W. P. Blake.— The raised reefs of Fernando de Noronha, 

 by Henry N. Ridley. — The cause of active compressive 

 stress in rocks and recent rock flexures, by T. Mellard Reade. 

 —A new phosphate from the Black Hills of South Dakota, 

 by W. P. Headden. — Note on certain peculiarities in the 

 behaviour of a galvanometer when used with the thermopile, by 

 Ernest Merritt. — Supplementary notice on the polycrase of 

 North and South Carolina, by W, E, Hidden and J. B. 

 Mackintosh. 



The American Meteorological Journal for March contains : — 

 An article by S. M. Ballou, on Prof. Russell's theory of cold 

 waves, published in the Report of the Chief Signal Officer for 

 1889. This article is a reprint of a paper read at the meeting of 

 the New England Meteorological Society on January 20 last. 

 According to Prof. Russell's theory, the cause of the cold area 

 from which the cold wave is drawn is held to be a preliminary 

 strong upward diminution of temperature in the air, a subsequent 

 overturning, bringing the cold air to the surface and producing 

 uniform temperature upwards, and a further cooling above, 

 producing high pressure. The author points out that each of 

 these assumptions would probably be questioned, and he 

 considers each of them in detail, quoting from the works of 

 various authorities upon the subject. — Temperature in high and 

 low areas. This is a translation of the substance of a reply by 

 Dr. Hann, in the Meteorologische Zeitschrift of September 1890, 

 to the criticisms of Prof. Hazen. These papers have already 

 been noticed at length in Nature. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, April 30. — "The Passive State of Iron and 

 Steel, Part III." By Thos. Andrews, F.R.S., M.Inst.C.E. 



Series V., Set i. Relative Passivity of IVr ought -iron and 

 various Steel Bars, and the Influence of Chemical Composition 

 and Physical Structure on their Passive State in Cold Nitric 

 Acid. — The passive state of iron or steel may have hitherto been 

 regarded by many as a sort of fixed property pertaining to iron 

 and steel alike, when immersed in cold strong nitric acid. The 

 following experiments were made to investigate if the passivity 

 was of a universally static character, or whether it varied with 

 the chemical composition and general physical structure of the 

 metal, and, if so, to what extent. 



The experiments of Series V., Set i, were made on bars of 

 the various steels selected from the author's standard samples. 

 The bars were cold drawn through a worile, and were therefore 

 different in physical structure to the rolled plates used in the 

 second series of the experiments. An idea of their general 

 properties will be obtained on reference to Part II., Tables IV. 

 and V. A polished bar, Z\ inches long, 0'3io inch diameter, 

 of the steel to be tested was placed in the wooden stand w, 

 along with a polished wrought- iron bar of equal size, and 

 the pair were then immersed in 1-4 fluid ounce of nitric acid, 

 I "42 sp. gr., contained in the U-tube, the bars being in circuit 

 with the galvanometer. The immersion was continued for the 

 periods stated, and with the electro-chemical results given on 

 Table VI. 



The wrought-iron bars used in each experiment were cut from 

 one longer polished rod, so as to afford a fair comparison of the 

 relative passivity of the various steels, compared with the 

 wrought-iron and also with each other. The results are the 

 average of numerous experiments in each case. 



The experiments of Series V., Set i, on the relative pa-sivity 

 of wrought-iron, soft cast-steel, hard cast-steel, soft Bessemer 

 steel, and tungsten steel, showed that wrought-iron was 

 €lectro-positive to the steels with a considerable E.M.F., the 

 wrought-iron being thus shown to be less passive than the 

 steels. 



Series V., Set 2. Relative Passivity of Wrought-iron and 

 various Steel Plates in Cold Nitric Acid, sp. gr. I "42. — In the 

 following series of observations, the metals experimented upon 

 consisted of plates of rolled wrought-iron, rolled steels made" by 

 the Bessemer, Siemens-Martin, or crucible cast steel processes, 

 such as soft cast-steel, hard cast-steel, soft Bessemer steel, hard 



Bessemer steel, soft Siemens steel, hard Siemens steel, and they 

 are of the chemical composition given on Table VII. The 

 terms "soft" and "hard" relate only to difference of per- 

 centage of combined carbon, and not to their having under- 

 gone annealing or hardening processes. Each plate was 

 3 inches square, by \ inch thick = total area of exposure 

 I9'5 square inches including edges, brightly polished all 

 over, and had a long thin strip left on the top side, for 

 convenience of attaching to the galvanometer connections. 

 The whole of the wrought-iron plates, used as elements with the 

 various steel plates, were cut from one larger wrought-iron plate, 

 and were thus practically of uniform composition, thus ensuring 

 an accurate comparison of the relative pas-ivity of the wrought- 

 iron compared with the different types of steels, and at the same 

 time indicating relatively the influence of varied composition 

 and structure on the passivity of the different classes of steels 

 under observation. In each experiment, a polished wrought- 

 iron plate and a polished steel plate were firmly placed in two 

 small holes drilled through a thick plate-glass cover ; the cover 

 holding the two plates was then carefully placed closely over a 

 porcelain vessel containing 15 fluid ounces of nitric acid, sp. gr. 

 I '42, the plates being fully immersed in the acid, and the 

 protruding shanks of the bars connected in circuit with the 

 galvanometer. The electro-chemical effects observed were then 

 taken in the usual manner, and the results are given in detail on 

 Table VIII., and indicated that wrought-iron was less passive 

 than the steels, and further demonstrated that steels of a higher 

 percentage of combined carbon are more passive than those of a 

 lower percentage of combined carbon. 



General Remarks. — It has been necessary to give in modified 

 detail the effects observed during the periods of experimentation 

 recorded on the Tables, Parts I., II., and III., so as to convey 

 an accurate intimation of the method and nature of the research ; 

 and a brief resume of some of the principal results and con- 

 clusions arrived at by the author up to the present time may now 

 be given. 



(i) The experimental observations of Part I., Series I., 

 indicate that the influence of magnetization on the passive state 

 of steel rods in cold nitric acid, sp. gr. i "42, is not very great, but 

 it was detectable with the delicate galvanometer and by the 

 sensitive electro-chemical method pursued by the author in the 

 investigation. 



The effect of magnetization is more marked in warm nitric 

 acid and when the iron is in a powdered state, as shown in the 

 independent and separate experiments of Messrs. Nichols and 

 Franklin on passive powdered iron in warm nitric acid, pre- 

 viously alluded to in Part I., by whom it was shown that the • 

 temperature of transition from the passive to the active slate was 

 very materially lowered by powerful magnetism ; their experi- 

 ments also indicate that the passive state of powdered iron 

 cannot be fully overcome, even under strong magnetic influence, 

 until a temperature of about 51° C. is reached. 



(2) The author's experiments of Part I., Series II., at higher 

 temperatures, confirm those of Part I. , Series I. , and further tend to 

 demonstrate the influence of magnetization in somewhat lessening 

 the passivity of steel, showing that even previous to the critical 

 temperature point of transition from the passive to the active 

 state, magnetized steel bars were rather less passive in warm 

 nitric acid than unmagnetized ones. 



(3) The results in Part II., Series III., show that the passivity 

 of both unmagnetized wrought-iron and unmagnetized steel in 

 nitric acid, sp. gr. i "42, is considerably and proportionately re- 

 duced as the temperature of the acid increases, until the tem- 

 perature point of transition from the passive to the active state 

 is reached at a temperature of about 195° F., and it was also 

 found that the wrought-iron was less passive in the warm nitric 

 acid than cast-steel. (See also remarks at foot of Diagram I. 

 in Part II.) 



(4) The results of the observations of Part II., Series IV., 

 indicate that Scheurer-Kestner was, to some extent, in error in 

 regarding the passivity of iron as not dependent on the greater 

 or less degree of saturation -of the acid. The author's experi- 

 ments herein recorded have shown that the passivity of the 

 metals employed, viz. wrought-iron, soft cast-steel, hard cast- 

 steel, soft Bessemer steel, and tungsten steel, was very materially 

 increased with the concentration of the nitric acid ; and it was 

 also observed that wronght-iron was much less passive in the 

 nitric acid of less concentration than most of the steels, the soft 

 Bessemer steel being found about equal in passivity to the 

 wrought-iron under the conditions of experimentation. A re- 



NO. II 26, VOL. 44] 



