ON THE 13XPL03IBILITY OF COAL OILS. 101 



for burning in lamps ; and it cannot be advantageously reduced to 

 vapour to be mized with coal gas, because it does not form a permanent 

 gas ; for the vapour, like that of alcohol, becomes condensed to a liquid 

 whenever it is cooled, as occurs on its passage through cold iron gas- 

 pipes under ground. The only available use of naphtha is for dissolv- 

 ing India-rubber, and for mixing with painters' oil as a substitute for 

 spirits of turpentine. For these reasons naphtha is nearly worthless for 

 sale in the market ; and as it constitutes ten or fifteen per cent, of the 

 petroleum used for distillation, there is a strong temptation to the 

 distillers to divert the current of naphtha into the kerosene oil- 

 cistern to gratify the cupidity of purchasers by thus affording the oil 

 at a low price. Thus both sellers and buyers are alike tempted to 

 disregard the danger resulting from mixing the naphtha with the kero- 

 sene oil. 



To gratify purchasers of coal oil by an extraordinary low price, it 

 has been stated that dealers have contracted for the waste naphtha and 

 residuary heavy coal or tar for preparing a mixture of about the same 

 specific gravity as kerosene oil, and resembling it in appearance. The 

 hydrometer is not, therefore, available for detecting this spurious article, 

 and there remains no other mode of ascertaining its dangerous cha- 

 racter than by actually testing its inflammability experimentally by 

 the degree of heat indicated by a thermometer, at which it will become 

 kindled by the application of a lighted match, and begin to exhibit a 

 lambent flame flickering over its surface, as over that of blazing alcohol. 

 If the sample of oil contains much naphtha, it will be found capable of 

 emitting sufficient gaseous vapour to take fire at the ordinary tempera- 

 ture of the air on plunging a burning match in a cup of the oil. Other 

 samples will require to be heated at 90 deg., and even to 160 deg., be- 

 fore they can be similarly kindled. There is all this difference in the 

 inflammability of the article sold in the market for coal oil. Judging ot 

 all the qualities of coal oils by some few cases of the explosive inflam- 

 mability of the lowest grade in the market, they have all been subjected 

 alike to doubts and suspicions. As the coal oils offered for sale by 

 establishments of known respectability are really most valuable and eco- 

 nomical substitutes for whale oil for purposes of illuminations, it is 

 unwise, as well as unprofitable, to embrace them all in one sweeping 

 clause of condemnation without experimental examinations to determine 

 the facts in relation to this novel subject of inquiry. 



The presence of naphtha in kerosene oil essentially contributes to 

 the brilliancy of the light for illumination, whilst at the same time 

 it improves the combustibility of the oil by a less tendency to emit 

 smoke. It is, therefore, for the interest of the consumer of coal oil to 

 retain as much of this light volatile spirits as can be safely used ; for it 

 really seems like throwing away bread to reject so valuable an element 

 of human comfort and enjoyment available as a source of light and 

 warmth. The present waste of this material, which is now suffered to 



