_The Use of Oil, or Other Non-Gaseous Fuels._--Although gas, when available, is usually preferred on account of its convenience, there are several other fuels which give a hotter flame. They have, also, the additional advantage of not requiring any connecting pipes; but each has its own disadvantage. One liquid fuel deserves special mention as being rather less desirable than the others; this is alcohol. Although very convenient in use, it has the disadvantage of being rather too highly inflammable and capable of burning without a wick, thus involving a certain fire risk; the flame is scarcely visible in a bright light, and the heat given by either the ordinary flame or the blowpipe flame produced from alcohol is considerably less than that from a similar flame in which coal gas is used. For small work, however, the facility with which a spirit lamp may be lighted may more than counterbalance these disadvantages at times. _Paraffin Wax._--Where there is no coal gas available and the blowpipe is only required at intervals, and especially where high portability is required, there are few fuels so convenient as paraffin wax. This may be obtained in pieces of a satisfactory size by cutting paraffin candles, from which the wick has been withdrawn, into lengths of about half an inch. These cut pieces have the advantage over any oily fuel, such as colza oil, that they can be wrapped in paper or carried in a cardboard box; further they will keep indefinitely, even in the presence of air, without undergoing any perceptible change. _Forms of Lamp for Paraffin Wax._--Probably, the best form is that devised by Thomas Bolas, and described by him in the _Journal of the Society of Arts_, December 2nd, 1898. This lamp consists of a small open tray of iron, through which pass three or more flat tubes, and between these tubes are placed small flat pieces of wick, the fit being such that the pieces of wick may be adjusted easily by means of a pair of pointed tweezers. The flame thus obtained, instead of having one large hollow, is broken or divided so that the combustion is concentrated into a smaller area, and the air blast, which is directed across the flame, carries the flame with it in a more complete manner than is the case with the ordinary flame; a more thorough combustion being realised by this arrangement. Another advantage is the ease with which the wick may be changed and a larger or smaller wick inserted to suit the flame to any size of air jet. This form of lamp may be used for oily fuel, although it is specially suitable for paraffin wax. Two small pieces of bent tin-plate may be used as side covers, and these serve to adjust the flame within certain limits. A tin-plate cover which fits easily over the whole lamp serves as an extinguisher. The complete lamp is shown by _d_, Fig. 16, and this figure shows also a quick-change air-jet device, the whole arrangement forming a blowpipe for use where a non-gaseous fuel is to be employed.