CHAMBERS'S INFORMATION FOR THE PEOPLE. 



flame. With this view, glass chimneys are often 

 made to contract a little above the top of the 

 flame. 



Another difficulty attending the use of the ordi- 

 nary animal and vegetable oils in lamps arises 

 from the change of level in the oil. This is 

 sought to be remedied by making the vessel wide 

 and shallow ; and in order that it may cast as 

 little shadow as possible, it is disposed in the form 

 of a wide ring round the burner. But the most 

 effectual plan is to have the oil pumped up from the 

 foot of the lamp to the wick by mechanical means. 

 The most perfect mechanical lamp is that of Carcel, 

 a Frenchman, in which the oil is pumped up by 

 clockwork ; it is, however, by far too expensive and 

 difficult of repair to be adapted for ordinary use. 

 The French Moderator Lamp is much simpler, 

 and appears to overcome the difficulties of the 

 case. The body of this lamp consists of a cylinder 

 or barrel, the lower part of which contains the 

 store of oil. On the top of the oil rests a piston, 

 which is constantly pressed down bya spiral spring, 

 situated between it and the top of the barrel. 

 Through the piston is inserted a small tube, which 

 passes up to the burner at the top ; and the pres- 

 sure of the spring on the piston causes a constant 

 stream of oil to rise up through this tube and feed 

 the wick. What is not consumed flows over the 

 burner, and back into the barrel above the piston. 

 It is above the piston also that fresh oil is intro- 

 duced. When the piston has reached the bottom, 

 it is wound up again by a rack and pinion, and a 

 vacuum being thus formed, the oil above it is forced 

 to the under side through a valve kind of contriv- 

 ance round its edge. 



It is obvious that in this machine the flow of oil 

 will be greatest when the piston has been newly 

 wound up, and the spring is at its greatest tension. 

 This inequality is regulated, or moderated hence 

 the name of the lamp by an extremely ingenious 

 contrivance, which narrows the passage for the 

 oil when the pressure is strongest. 



The introduction of mineral oils known under 

 the various names of paraffin oil, petroleum, kero- 

 sene, naphtha, shale oil, &c. has in a great measure 

 superseded the use of animal and vegetable oils 

 for lighting purposes. The great recommendation 

 of the former is their cheapness. One great dif- 

 ficulty with the mineral oils at first was that, without 

 careful preparation, they are apt to give off inflam- 

 mable vapours at a low temperature, which give 

 rise to dangerous explosions. This has been ob- 

 viated by processes of rectification which get rid 

 of the lighter and more volatile ingredients. An 

 oil that gives off an inflammable vapour at a tem- 

 perature under 120 F. can hardly be considered 

 safe. Paraffin oil from Boghead coal will not 

 form an explosive mixture under 140 F. (See 

 USEFUL MINERALS, p. 389.) It is illegal to store 

 or issue oil forming an inflammable mixture 

 under 100 F. Another difficulty was to make 

 the oil burn without smoke. The kind of lamp 

 found to effect this purpose best was introduced 

 into Great Britain from Germany about 1856, 

 and, with minor improvements, the form is still 

 adhered to. The body of the lamp is a globular- 

 shaped reservoir of glass or stone-ware for the oil, 

 mounted on a foot or pedestal ; into this a brass 

 wick-holder is screwed, the wick being raised or 

 lowered by means of a rack and pinion. The pecu- 

 liarity of the paraffin lamp is a dome-shaped cap 



492 



surrounding the wick-tube, and having a slit run- 

 ning across it, through which the flame issues. A 

 long glass chimney rests on a ledge or gallery 

 around the base of the cap ; and by perforations in 

 the brass an air-chamber is formed below. The 

 chimney causes a strong draught through this 

 chamber, and the cap or dome deflects the current 

 of air, and makes it impinge against the flame as 

 it passes through the slit, thus producing perfect 

 combustion and a white, brilliant light without 

 smoke. The oil is so volatile that the flame has a 

 very slight hold of the wick, so that, if properly 

 burned, six inches of wick will last a year. The 

 demand for these lamps has become so great, 

 especially in America, where gas is expensive, 

 that the manufacture and sale of them forms an 

 extensive business of itself. 



A great drawback in the use of the common 

 paraffin lamp is the expense and annoyance attend- 

 ant on the frequent breakage of the glass chimney. 

 To obviate this, Rowatt and Son of Edinburgh 

 have introduced their patent Anucapnic (smoke- 

 less) lamp, which dispenses with the glass chimney 

 altogether. Instead of it, a second cap or dome is 

 placed over the ordinary one, leaving a narrow 

 space between the two. As the two cones get hot, 

 a powerful draught is created, and two separate 

 currents of air are directed against the flame, one 

 by the lower cap, as in the ordinary lamp, and 

 the other from between the two caps. The result 

 is perfect combustion, without a chimney. A large 

 glass globe is used to protect the flame from 

 currents of air, as well as to disperse and soften 

 the light. Such a globe is also often used with 

 the ordinary lamp in addition to the chimney, a 

 flange for supporting it being added to the burner. 

 Fig. ii represents the smallest form of paraffin 



Fig. ii. 



lamp. A section of the burner is represented 

 at a. The double domed lamp is represented in 

 fig. 12. 



Fig. 12. 



Mineral oil thus burned furnishes a satisfac- 

 tory light, rivalling gas in cheapness (see page 

 496). 



