These are, as well known, operated generally by the production of sparks from a flint by the rotation of a toothed wheel, or by means of a metal striker or scraper; the sparks, falling on to a wick soaked more or less with petrol, cause this to catch fire. It is by no means uncommon to see the user unable to quickly get a light even in a place free from draughts. This will be due to one or other of the following causes : (1) Not enough petrol or wick in the container; (2) The toothed wheel is not sharp enough

(3) ;the flint is nearly worn away and jams when the wheel is rotated, or it may stop and lock the wheel :

(4) ;The flint passage or tube has become oval at the top end or (5) owing to incorrect design the level of the sparks is not correct for the level of the wick. As the toothed-wheel design can be made to operate, and light the wick every time, given proper condition the device is very convenient and well worth getting right. Cause (1) is easily tested for; even the cheapest brand of commercial petrol should light easily, and a longer length of wick can easily be put in if required. Cause (2) is one of the most frequent troubles, and generally not suspected, since the teeth may look fairly sharp, and cause a shower of sparks, but it would seem that the sparks caused by a blunt wheel have not the intensity required to ignite the petrol, and the generally attempted remedy is to rotate the wheel faster and cause a larger shower of sparks or to increase the pressure of the flint upon the wheel. If, however, the wheel be taken off, generally by knocking out a rivet, softened by heating to a bright-red and allowing to cool, resharpened by a fine half-round or three-corner file, so as to produce teeth like those of a wood saw facing the direction of rotation, heated to a bright red and dipped into cold water, and then replaced in the correct position, i.e., teeth facing the right way, which is in the direction of rotation, it will be found that the wick will light every time, even when the wheel is rotated only slowly and to a slight amount.

Cause (4) is a frequent reason of jamming, even with a new flint, and is caused by either the flint being too easy a fit in its passage or tube, or owing to pressure and wear the tube end has become oval. The remedy is to make it round again, and only just a free fit on the flint, the method of doing this depends upon the design of the lighter, generally it is possible to let in a metal tube of the right size, and solder it into position. Cause (5) is not often the trouble, but it should be looked for and corrected if necessary so as to bring the top level of the flint in a line with the centre of the vertical protruding wick.

Given, however, that the supply of petrol, wick and flint are correct, the most frequent cause of trouble is a blunt wheel, and next to this the jamming of the flint against the wheel and preventing rotation.

The flints which appear to be so called for want of a better word are cylindrical in shape, generally about 5 m/m long by about 3 m/m diameter, and contain a large proportion of cerium. Alloys of cerium with either 30 per cent, of iron or 12 per cent, of magnesium spark with slight friction. Boron and titanium also will form alloys with cerium and give the same effect.

A recent patent provides for a perforated shield around the end of the wick, but having an opening such that the flint sparks can reach to wick. This improvement makes it difficult for the flame to be blown out by a draught, and also seems to considerably lengthen the life of the wick as the flame appears to be that of the ignited petrol vapour above the wick, and not actually in contact with the wick, the wick there-lore does not burn or char.