128 



NA TURE 



[December 12, 1901 



The Influence of Temperature on the Action of 

 Nitric Acid on Metals. 



The following simple buL striking experiments illustrating 

 the influence of temperature upon the action of nitric acid on 

 metals may possibly be of interest to those who are engaged 

 in the teaching of chemistry. 



If three tubes containing strong nitric acid are cooled tielow 

 — 10* C. by means of a freezing mixture of snow or pounded ice 

 with salt, and then copper turnings added to one, granulated zinc 

 to another and magnesium ribbon to the third, it will be found 

 that no action takes place, the nitric acid being practically inert 

 at this temperature. If the tulies are then exposed to air at 

 about 22° C. so that the temperature rises slowly, it will be 

 found that little or no action occurs until a certain temperature 

 is reached, when a sudden and violent ebullition of brown fumes 

 occurs, the metal rapidly dissolving and the temperature abruptly 

 rising from 80° C. to as much as 104° C. 



The critical point for this violent action lies in the case of zinc 

 between o^ C. and 2° C, in that of magnesium between 17° C. 

 and 19" C, and in that of copper between 19° and 21° C. 

 Before these temperatures are reached very feeble action may 

 occur and a few bubbles of gas be disengaged, especially in 

 the case of the zinc. These bubbles consist partly of hydrogen 

 gas, and if magnesium is added to cold dilute (\-\) nitric acid 

 an active evolution of nearly pure hydrogen takes place at first, 

 although as the solution becomes warm and the percentage of 

 magnesium nitrate increases, the production of hydrogen rapidly 

 diminishes. This is in somewhat striking contrast to the 

 common statement in chemical text-books to the effect that 

 in no circumstances can hydrogen be obtained by the action of 

 nitric acid on metals. Alfred J. Ewart. 



Meteorological Work for Science Schools. 



I r has often occurred to me that the collection of data, such 

 as those necessary for the investigation of fog distribution, might 

 well be entrusted to the science schools over which the 

 Technical Education Board of the London County Council 

 exercise control. 



There is, in such a research, that element of originality which 

 is needed in the work of our school laboratories. 



For interpretation the collected data may afterwards be distri- 

 buted to the schools engaged in the work. 



I foresee only the difficulty due to the intervention of 

 vacations. J. ^'. H. CoATES. 



41, East Uulwich Grove, S.E., November 25. 



[We have referred the foregoing letter to the Secretary to the 

 Meteorological Council, who has been good enough to send 

 the following remarks upon it. — Editor, Nature.] 



The primary difficulty in the way of using science schools, as 

 suggested by Mr. J. V. H. Coates, for the immediate purposes 

 of such an inquiry as that of the distribution of fogs is that the 

 schools have fixed hours of attendance to which the fogs pay no 

 heed. To carry out such an investigation effectively the twenty- 

 four hours must be taken into account. Of course the imjuiry 

 might be restricted to those fogs which begin or end within the 

 hours of attendance, but that would be a very .serious limitation. 

 As confirmatory evidence, careful observations within school 

 hours might be very useful. The necessity for securing a suit- 

 able uniformity among observers as regards the terms employed 

 in the estimation of fogs makes it necessary, however, to proceed 

 with caution in extending the number of separate observers. 



The kind of cooperative investigation which is appropriate 

 for organised science schools is one which can be dealt with 

 primarily by observations at fixed hours. On special occasions 

 it might doubtless be pursued beyond those hours in following 

 up some definite point. Several inquiries of this nature may be 

 suggested. For example, in relation to the fog inquiry, it is 

 desirable to know something of the effect of wet ground during 

 rapid falls of temperature. For this purpose an investigation of 

 the temperature of wet soil or sand suitably exposed and its 

 relation to the temperature of the air would be a very useful 

 adjunct to the ordinary meteorological data. It is a part of the 

 inquiry more suitable for science schools than for routine ob.ser- 

 vation, because the conditions of exposure require examination 

 and consideration as well as the readings of the thermometers. 



NO. 1676, VOL. 65] 



The hours of non-attendance could be bridged by registering 

 minimum instruments or, in some enterprising schools, by self- 

 recording instruments, the development and investigation of 

 which would be in themselves a useful study. 



Another line of cooperative inquiry, of much greater diffi- 

 culty, suggested to me in various forms by several scientific 

 friends, has reference to the large amount of fuel consumed daily 

 within the London area. The combustion must of necessity 

 raise the temperature o( the air in or over London above that of 

 its surroundings. The raised temperature should give rise on 

 calm days to a diminished pressure and an inflowing air current. 

 Ordinary meteorological observations are not of a sufficiently 

 high order of accuracy to exhibit these effects, but by coopera- 

 tive, and in the best sense competitive, effort between science 

 schools in different parts of the metropolis progressive steps 

 could be reached which might ultimately have the very satisfac- 

 tory result of exhibiting quantitatively the effects of the local 

 heating. If this ultimate purpose should not be achieved, the 

 light thrown upon the practicable limits of observation would 

 not be without interest. 



Then, again, the chemical composition of air at different 

 points during foggy days would be a useful inquiry. Probably 

 the results obtained at the first attempt would not be accepted 

 as final, but the discussion of the results from different centres 

 would lead to more accurate determinations and ultimately to 

 definite information of substantial value. Incidentally, such co- 

 operative inquiries would be of very great educational influence 

 and advantage. Supposing, for example, that it were decided 

 to make observations of any rapidly varying element at a definite 

 point of time, the mere carrying out of the comparison of the 

 time-keepers at the different schools would be most in.structive. 

 The comparison of their length-standards with a view to accurate 

 barometric measurement might be beyond the reach of available 

 apparatus, but even the demonstration by appeal to experience 

 that the best comparisons that could be eft'ected with the appa- 

 ratus at command, left a margin of inaccuracy of a certain defined 

 magnitude would be sufficiently instructive to make the experi- 

 ment worth trying. W. N. Shaw. 



November 30. 



The Date of Stonehenge. 



The remarkable paper on Stonehenge, by Sir N. Lockyer 

 and Mr. Penrose, in Nature of November 21 has greatly in- 

 terested me. Just two years ago I was working at the subject, 

 and wrote to Prof Petrie to inquire what azimuth he had used 

 for the axis of the temple in his estimate of the date, which he 

 gives as 730 a.d. + 200 years, with a possible date of 400 A. I>. 

 As I received no reply I employed the angle 50 12' E. of N., 

 given in Mr. Edgar Barclay's "Stonehenge," 1S95. With this 

 azimuth I obtained by means of a formula, kindly supplied by 

 Dr. Downing, F.R.S., a date of 425 A.D. I find that, for the 

 given azimuth, even this date is too early, as I did not allow 

 enough for refraction, &c. Applying the .same formula to the 

 figures given in Sir N. Lockyer's paper, the date comes out about 

 1700 H.C., as stated, so that the formula was correct, and the 

 chief error was in the erroneous azimuth of the axis, which 

 differs by about 38' from the 49 34' iS" so carefully determined 

 in the published paper. Now as an increase of some 90" in 

 sunrise azimuth at the solstice means a decrease of some 46" in 

 declination and represents the lapse of about a century, the dis- 

 crepancy is clearly explained. Allowing for refraction, t\:c. , 

 I make the present azimuth of the sun at sunrise at the 

 solstice about 50^ 26' 21" E. of N., the sun's declination being 

 23° 27' 8" N. Consequently since the date, 1700 B.C., the 

 solstitial sunrise azimuth h.as shifted 52' 3 " further E. and the 

 declination has decreased 27' 22", representing a lapse of about 

 3600 years, when the appropriate formula is applied. 



At the distance (250 feet) of the Friar's Heel, or Sun-stone, 

 from the centre of the ruin, a change in azimuth of 52' would 

 shift a point on the axis only 3 feet 9 inches, and, as the avenue is 

 50 feet wide, some idea may be formed of the necessary delicacy 

 of the meisurements. The azimuthal shift of the sun himself is 

 less than two diameters. It seems to me very improbable that 

 any estimate of the date closer than that arrived at by Sir N. 

 Lockyer and Mr. Penrose can be made on astronomical grounds. 

 Recent excavations have given valuable information, but much 

 more yet remains to be done in this direction. I may add that 

 an exhaustive study of the " Blue-stones" (igneous rocks foreign 

 to the locality) by the methods of modern petrology may lead to 



