56 REPORT—1858. 
carbon rod; but whenever the voltaic current is allowed to circulate, the electro- 
magnet is formed and its armature is drawn up; a ring connected with the armature 
compresses the halves of a hollow wedge; the upper edges of the wedge fix into the 
grooves in the file-like rod with its attached carbon, and in the general movement 
upwards the latter is slightly raised from the lower carbon, and the light is instantly 
roduced, 
It will thus be observed, that the ring attached to the armature performs two offices 
when drawn up towards the elecitro-magnet:—in the first place, rising from a narrower 
part, where it loosely surrounds the hollow wedge, it tightly embraces, when half- 
mast high, the wider part of the wedge, and compels it to set in tightly to the file-like 
rod; and in the second place, having firm hold of the wedge, it drags up that part 
with the now adherent roughened rod and upper carbon, and holds these suspended 
at the proper distance. ‘The light continues to burn steadily till the charcoal points 
by combustion and the transference of carbon have their proper distance from each 
other increased to that point when the electricity ceases to flow; then the electro- 
magnet loses its attracting power, the armature and the attached ring fall down; the 
halves of the wedge, separate from each other, loose their hold of the file-like rod, and 
allow the Jatter to descend by the force of gravitation, till the upper charcoal pencil 
touches the lower carbon rod, when instantly the electrical current is re-established, 
the magnet is reformed, and the upper carbon is again drawn up. So momentarily 
does this extinguishing and relighting of the lamp occur, that the interval of darkness 
is hardlybservable to the naked eye. In duration of time, as also in the convulsive 
throb which the moveable parts of the apparatus then give, the phenomenon greatly 
resembles the beat of the heart of an animal. The lamp may be accommodated to 
any size of battery sufficient to show the light. By means of a series of screws in 
connexion with the armature, and the supporting arm, the moveable and adjusting 
part of the lamp may be lowered from the electro-magnet or raised towards it, If 
the battery be small, then the lifting arrangement is screwed up near the magnet ; 
whilst if the battery be large, and a corresponding amount of electricity at command, 
the regulators are placed further from the lifting power, and when the voltaic cur- 
rent traverses the arrangement, the moveable carbon is drawn up a greater distance, 
more space is presented between the carbon poles, and necessarily a longer and more 
dazzling arc of flame is formed. 
On M. de Luca’s Claim to be the Discoverer of the Non-Presence of Iodine 
in the Atmospheric Air, Rain-Water, and Snow. By Dr. Srevenson 
Macapam. 
Note on the Production of a Frosted Surface on Articles made of Aluminium. 
By Stevenson Macapay, Ph.D., F.RSE., F.C.S., Lecturer on Che- 
mistry, Surgeons’ Hall, Edinburgh. 
The attention of the author was directed to this subject, on the occasion of pre- 
paring several class medals from the rare metal aluminium. The metal was obtained 
direct from Paris in small ingots. ‘The die-stamper in this country fused the bars of 
aluminium and recast the metal in a form of ingot mould, more suitable for the after 
operations. The metal bars thus obtained were subjected to rolling, then annealed, 
and the medals struck. Every care was taken to have the die perfectly clean and 
highly polished, and yet the medals were always obtained with a tarnished appear- 
ance on the surface, which rendered still more unacceptable the blue xine hue which 
the aluminium presents when most free from surface blemishes. An attempt was 
made to get rid of the tarnished surface by friction or polishing, but this did not 
sensibly remove the stains. It was then resolved to frost the medals in the same 
way as silver articles are frosted, viz. by the employment of hydrochloric acid into 
which the heated metal is dipped; but the action of acids on aluminium was so slow, 
aes they failed to produce the requisite effect, and their employment was dispensed 
with. 
The author then introduced the aluminium articles into a solution of caustic potash 
raised to a temperature above blood-heat, which immediately attacked the metal, 
