December 9, 1922] 



NA TURE 



111 



critical range (700 C.) and cannot be said to have any 

 definite strength at a red heat, and that the property 

 of principal importance to the engineer who wishes to 

 subject highly heated steel to stress is the equivalent 

 of the viscosity of a fluid. For the solution of a problem 

 of immediate practical importance, he has ascertained 

 for each of a number of steels the temperature at which 

 the rate of flow does not exceed a very small and 

 practically negligible amount under a uniform stress 

 of 8-5 tons per square inch. The particular problem 

 was the manufacture of large catalyst tubes for a 

 synthetic ammonia process. These tubes were to be 

 maintained at a temperature of about 6oo° C. under 

 an enormous internal pressure, a long life under these 

 conditions being essential to the economic success of 

 the process. After due consideration it was decided 

 to make them of a nickel-chromium alloy which was 

 known to possess high resistance to oxidation and 

 deformation when under stress at high temperatures. 



Laboratory tests were carried out on this alloy, on 

 pure carbon steels, on a high chromium steel, and a 

 high-speed steel. For details of the actual experiments 

 the original paper must be consulted. It must be 

 noted, however, that although the mechanical con- 

 ditions chosen for the tests appear to have been con- 

 sidered with great care, there were considerable varia- 

 tions in the temperature of a given test-piece which 

 amounted to as much as + 25° C. from a mean figure. 

 Tests of two kinds were carried out : (a) those at 

 constant load and constant temperatures, and (b) those 

 at constant load and uniformly rising temperature. 

 The extension temperature diagrams of the (b) series 

 show that up to 400 C. all the steels extended alike. 

 Thereafter, however, the curves diverged, a consider- 

 able amount of flow taking place in each case, at tem- 

 peratures well below that finally reached. The range 

 of temperature investigated extended up to nearly 

 iooo c C. 



The diagrams of the (a) series present some remark- 

 able results, of which perhaps the most striking was 

 that of the test-piece of nickel-chromium alloy (Vikro), 

 which extended continuously from the first day of 

 loading (at 625° C.) but only broke after 36 weeks. 



The diagrams bring out well the enormous influence of 

 time in determining the temperature up to which each 

 type of steel can support a given load (in this case 8£ 

 tons per square inch), and by implication a load 

 which can be borne at any given temperature. As an 

 example, a nickel-chromium alloy withstood the above 

 stress under a rapidly applied load at 965 C, whereas 

 the same specimen cannot be expected to endure the 

 same stress for considerable periods without suffering 

 sensible deformation at a temperature exceeding 6oo° 

 C. Working conditions such as those outlined demand 

 a knowledge of the latter figure. 



Mr. Dickenson concludes from his tests that the 

 extension and eventual rupture of the test-piece 

 under unvarying load is due almost entirely to viscous 

 flow. Whether plastic flow affects the shape of the 

 curves, and if so, whether the data will prove sufficient 

 to enable the plastic to be separated from the viscous 

 flow, is a question to which he has not yet found an 

 answer. His curves are also interesting for the light 

 which they throw upon the differing degrees of resist- 

 ance to mechanical deformation at high, temperatures, 

 which the various steels exhibit. Moreover, in select- 

 ing material for resistance to stress at these tempera- 

 tures, the nature of the stressing action must be taken 

 into account. 



In the second half of his paper, consideration is given 

 to the very important factor of resistance to " scaling " 

 exhibited by steels at the temperatures in question. 

 It has been known for some time that remarkable 

 resistance to oxidation is offered by certain nickel- 

 chromium alloys, and, in a somewhat less degree, by 

 high chromium steels. Mr. Dickenson has carried out 

 systematic experiments on eight typical steels, in nine 

 temperature ranges from 55o°-6oo° up to io7s°-ii75 C. 

 The best results were given by a nickel-chromium alloy 

 called " Vikro." Interesting photomicrographs are 

 furnished, showing the varying character of the scale 

 in the various alloys. Mr. Dickenson's research will 

 be welcomed by chemical and metallurgical engineers, 

 for it contains valuable information for which they 

 have long been waiting. It is much to be hoped that 

 he will see his way to continue his experiments. 



The Manufacture of Acids during the War. 1 

 By Prof. T. M. Lowry, F.R.S. 



THE three technical reports before us deal with 

 the manufacture of sulphuric, nitric, and 

 picric acids during the war. The reports are compiled 

 on similar lines to those of the four earlier volumes which 

 have already been reviewed in these columns (Nature, 

 April 29, 1922, p. 541) ; and since the methods and 

 workmanship of Mr. W. Mai nab are now well known, it 

 is not necessary to describe in detail the type of in- 

 formation which they contain. It maw however, be 

 of interest to review briefly the general situation as 



1 Ministry of Munitions and Department of Scientific and Industrial 

 Research. Technical Records of Explosives Supply, 1915-1918. No. 5 : 

 " Manufacture of Sulphuric AcicLby Contact Process." Pp. vi + 12S + plates. 

 (London: H.M. Stationery Office, 1921.) 25s. net. No. 6: "Synthetic 

 Phenol and Picric Acid." Pp. vi-r-97 -i-plates. (Loudon: H.M. Stationery 

 Office, 1921.) 15s. net. No. 7 : " Manufacture of Nitric Acid from Nitre 

 and Sulphuric Acid." Pp.vi + 86. (London: H.M. Stationery Office, 1922.) 

 10s. 6d. net. 



regards supplies of acids which had to be met by the 

 Department of Explosives Supply, and the way in 

 which the problem was solved by the workers of that 

 Department, as disclosed in these three reports. 



Nitric Acid. 



Although oxidised nitrogen was the key of the 

 supplv-problem in explosives — both propellant and 

 11.1.. (just as chlorine was the basis of the supply- 

 problem in gas-warfare in its successive phases 

 of chlorine, phosgene, CC1 3 N0 2 , S(C 2 H 4 C1).,. or 

 mustard gas, etc.) — the report on the manufacture 

 of nitric acid is undoubtedly the least important of 

 tin m three, since it is much to be hoped that this 

 country will never again be dependent on overseas 



NO. 277I, VOL. I IO] 



