July 6, 1888.] 



SCIENTIFIC NEWS. 



slip of supple cardboard, or a dry finger. When the 

 mixture is very intimate, the magnesium is added, and 

 the whole is thrown upon a piece of coarse muslin of an 

 open texture, placed upon a sheet of paper, upon which 

 the powder may fall on shaking the muslin. When this 

 operation has been repeated three or four times, the 

 mixture is ready to be converted into pastilles in the 

 following manner. The powder is placed upon a flat 

 piece of glass, ordinary collodion is added enough to 

 form a thin paste, which is mixed up with a wooden 

 spatula or with the finger. 



When the paste begins to set, it is at once formed into 

 a flat pastille, and when half dry it is detached from the 

 glass by passing beneath it the blade of a thin knife. It 

 is then dried as quickly and perfectly as possible, since 

 moisture would retard the combustion. The inventor 

 has preserved such pastilles for two or three days by 



Fig. 1. 



coating them with tin-foil paper, but he prefers to pre- 

 pare each morning a quantity sufficient for use in the 

 ensuing night. These pastilles have, as compared with 

 the powder, the advantage of not scattering burning 

 magnesium, and almost all the fumes remain shut up in 

 the apparatus. 



The following is the description of the apparatus in 

 which the powder or pastilles should be burnt. 



It is a box, placed vertically. The lid is replaced by a 

 slide, and the bottom board by a plate of tin, sloped at 

 30 (fig. 1). In the middle of this tin plate there are 

 pierced two small holes, to receive, the one a fuse 

 of gun-cotton, and the other a nail which is intro- 

 duced from below and which is twisted into a hook 

 inside the box. The upper part of the box is partly 

 removed, and this aperture is closed, at the moment of 

 operating, with four folds of moistened linen. Lastly, 

 the apparatus is lined with silver-paper, after the 

 fashion of a passe-partout. To have a complete appara- 

 tus, it is merely necessary to mount the whole upon a 



sliding support, which can be raised or lowered at will 

 (fig- 2). 



After having focussed by means of candles, place the 

 apparatus just described to the right or to the left of the 

 camera, and so high that the light may fall upon the 

 principal object at an angle of 15°. On the other side 

 of the camera there is a small support set on a plate 

 from which is suspended three or four ribbons of magne- 

 sium twisted together, and of a weight less, by fifteen 

 times, than that of the magnesium powder employed in 

 the apparatus. Care must be taken that the two foci 

 are out of the field of the object-glass. 



When these arrangements are made, the slide of the 

 apparatus is fitted with a thread attached to the bottom 

 of the trap, and which is fixed to the hook in the tin 

 plate after having passed into another hook at the upper 

 part of the box. There is then introduced through the 

 other hole in the tin-plate a fuse of gun-cotton, the 

 fibres of which are dusted over with the chlorate 



and magnesium powder, and the pastille is placed upon 

 it. The top of the box is then covered with the moistened 

 linen, and the operation is commenced. The magnesium 

 ribbons are ignited, the object-glass is quickly uncovered, 

 and when the magnesium is almost consumed the wick of 

 gun-cotton is kindled, taking care to keep behind the 

 apparatus. 



The pastille ignites and burns the thread which holds 

 back the slide, but this takes place only when the explo- 

 sion is complete, that is, after the explosion. At this 

 instant the object-glass is closed, and the proof is deve- 

 loped as usual. 



Fig. 1 shows the elevation of the apparatus, and fig. 2 

 the section. AA'A" is the slide, BB' the thread serving 

 to keep the slide raised, C hook to which the thread is 

 attached, D the focus, E the fuse of gun-cotton, S 

 the stand, L moistened linen placed over the openings 

 OO.' 



[It is essential that the chlorate of potash and the 

 sulphuret of antimony should be powdered separately. 

 Any attempt to pulverise them together, and even to mix 

 them with mortar and pestle, would, in all probability, 

 occasion a disastrous explosion. — Ed., Scientific News.] 



