330 



NATURE 



{Feb. 6, 1890 



for a smokeless powder suitable for field artillery and small 

 arms. 



The properties of ammonium nitrate, of which the products 

 of decomposition by heat are, in addition to water-vapour, 

 entirely gaseous, have rendered it a tempting material to work 

 upon in the hands of those who have striven to produce a smoke- 

 less powder, but its deliquescent character has been the chief 

 obstacle to its application as a component of an explosive agent 

 susceptible of substitution for black powder for service purposes, 

 A German chemical engineer, F. Gaus, conceived that, by in- 

 corporating charcoal and saltpetre with a particular proportion 

 of ammonium nitrate, he had produced an explosive material 

 which did not partake of the hygroscopic character common to 

 other ammonium-nitrate mixtures, and that, by its explosion, the 

 potassium in the saltpetre formed a volatile combination with 

 nitrogen and hydrogen, a potassium amide, so that, although 

 ■containing nearly half its weight of potassium salt, it would 

 furnish only volatile products. The views of Mr. Gaus regarding 

 the changes which his so-called amide powder undergoes upon 

 ■explosion were not borne out by existing chemical knowledge, 

 while the powder compounded in accordance with his views 

 proved to be by no means smokeless, and was certainly not non- 

 hygroscopic. Mr. Heidemann has, however, been successful, 

 by modifications of Gaus's prescription and by application of his 

 own special experience in powder- manufacture, in producing an 

 ammonium-nitrate powder possessed of remarkable ballistic 

 properties, furnishing comparatively little smoke, which speedily 

 disperses, and exhibiting the hygroscopic characteristics of am- 

 monium-nitrate preparations in a decidedly less degree than any 

 other hitherto prepared. The powder, while yielding a very 

 much larger volume of gas and water-vapour than black or 

 brown powder, is considerably slower than the latter ; the 

 ■charge required to produce equal ballistic results is less, while 

 the chamber-pressure developed is lower, and the pressures 

 along the chase of the gun are highei", than in the case of brown 

 powder. 



The ammonium-nitrate powder contains, in its normal, dried 

 condition, more water than even brown powder ; it does not 

 exhibit any great tendency to absorb moisture from an ordi- 

 narily dry or even a somewhat moist atmosphere, but if the 

 amount of atmospheric moisture approaches saturation, it will 

 rapidly absorb water, and when once the process begins it con- 

 tinues rapidly, the powder-masses becoming speedily quite pasty. 

 The charges for quick-firing guns are enclosed in metal cases, in 

 which they are securely sealed up ; the powder is therefore pre- 

 vented from absorbing moisture from the external air, but it has 

 been found that if the cartridges are kept for long periods in 

 ships' magazines, in which, from their position relatively to the 

 ships' boilers, the temperature is more or less elevated, some- 

 times for considerable periods, the expulsion of water from some 

 portions of the powder-masses composing the hermetically sealed 

 charge, and its consequent irregular distribution, may give rise 

 to want of uniformity in the action of the powder, and to the 

 occasional development of high pressures. Although, therefore, 

 this ammonium-nitrate powder may be regarded as the first 

 successful advance towards the production of a comparatively 

 smokeless artillery powder, it is not uniformly well adapted to 

 the requirements which it should fulfil in naval service. 



Attention was first seriously directed to the subject of smoke- 

 less powder by the reports received about four years ago of 

 remarkable results stated to have been obtained in France with 

 such a powder for use with the magazine rifle (the Lebel) which 

 was being adapted to military service. These reports were 

 speedily followed by others, descriptive of marvellous velocities 

 obtained with small charges of this powder, or some modifica- 

 tions of it, from guns of very great length. As in the case of 

 melinite, the fabulously destructive effects of which were much 

 vaunted at about the same time, the secret of the precise nature 

 of the smokeless powder was so well preserved by the French 

 authorities, that surmises could only be made on the subject 

 even by those most conversant with these -matters. It is now 

 well known, however, that more than one smokeless explosive 

 has succeeded the original powder, the perfection of which was 

 reported to be beyond dispute, and that the material now 

 adopted for use in the Lebel rifle bears, at any rate, great 

 similarity to preparations which have been made the subject of 

 patents in this country, and which are still experimental powders 

 in other countries. 



{To be continued.^ 



SOLAR HALOS AND PARHELIA. 

 'HTHE recent appearance of solar and lunar halos, parhelia, 

 ■*■ and paraselene, has called forth a considerable amount of 

 correspondence from all parts of the country, and the accompany- 

 ing figure may be taken as a composite representation of the 

 solar phenomenon observed. A glance at the times at which 

 the halos were observed on the 29th ult., makes it apparent that 

 they occurred earliest in places of highest latitudes. At Driffield, 

 in lat. 54°, the halo, with its attendant parhelia, was observed 

 at 1.34 p.m., and the whole phenomenon disappeared at 2.8 

 p.m. ; at Burton-on-Trent, lat. 52° 48', the halos and parhelia 

 were first observed at 2 p.m., and lasted more or less distinctly 

 until 3 p.m. ; whilst about a degree south of this, at Oxford, 

 Colnbrook, and Walton-on- Thames, the phenomena occurred 

 from about 3.30 to 4.30. The uniform difference in the times 

 when the halos were observed at the places of different latitudes 

 necessarily follows from the fact that they are formed by the 

 action upon solar rays of prismatic crystals of ice suspended 

 in the air by the ascending currents which especially occur in 

 the spring and autumn. Those prisms that are in such positions 

 that the rays from the sun in transmission through them suffer 

 minimum deviation are the cause of the formation of halos, and 

 since the angular distance of the sun equal to minimum deviation 

 is about 22°, this must be the radius of the halo, and the ex- 

 ternal circle, being produced by two such refractions in succession, 

 has a radius of about 46°. 



The halos recently observed do not differ in the main from 

 those frequently seen in higher latitudes, and consisting of (i) 

 a first circle or halo concentric with the sun, red within, violet 

 without, and at an angular distance of 22^ or 23° ; (2) a second 

 circle or halo, similar to the preceding, but at an angular dis- 



a was seen at 3.33 p.m. ; h at 3.45 p.m. : c and a? at 3.50 p.m. ; e at 4.0 p,m : 

 y at 4.10 p.m. 



tance of 46° ; (3) a portion of the parhelic circle appearing hori- 

 zontal and diametral, and at the points of junction of this circle 

 v/ith the two halos, there is increased luminosity, which have 

 been taken for images of the sun ; (4) horizontal arcs, tangents 

 to the circular halos, and a vertical line making a cross with the 

 horizontal portion of the parhelic circle, 



Mr. John Lovell thus describes the phenomena observed at 

 Driffield : — " A splendid solar halo, with its attendant parhelia, 

 was observed this afternoon at 1.34 local time. The halo 

 (diameter 45°) was almost perfect, the lower part only being 

 slightly obliterated by the thick atmosphere near the horizon. 

 Attached to the upper side, an inverted portion of a similar halo 

 appeared, brilliantly illumined on the concave side, the lower 

 part giving out a dull red light. Again, 22|° above this, and 

 also inverted, about 60° of arc beautifully coloured with rain- 

 bow colours was clearly visible, the red side lowest. This arc, 

 if it had been produced, would have circled the zenith. The 

 mock lights on each side of the halo were drawn out into long 

 cones of intensely bright light, while the inner sky of the halo 

 was of a very dark shade. The most noteworthy feature of the 

 display was a brilliant patch of pure white light in the north- 

 western sky, at a distance of 90° from the western mock sun, 

 and undoubtedly emanating from it, and which remained visible 

 for nearly ten minutes. The whole phenomena disappeared at 

 2.8 p.m., the sky then being covered with streaky cirro-stratus 

 haze from the north-north-west." 



The patch of white light referred to by Mr. Lovell was doubt- 

 less produced by the junction of the parhelic circle with one of 

 the halos concentric with the sun. It is perhaps hardly neces- 

 sary to note the relation that exists between halos and cirro- 



