M. Juste Preuss on Oil Gas. 205 



gas in shops, &c., is often complained of, and which, in effect, 

 is proportioned to the number of cubic feet which are hourly 

 burnt. It is almost superfluous to observe here that oil gas, 

 for equal light, gives no more heat than Argand lamps. To 

 all these advantages, oil gas also unites that of being the only 

 one which is suited for compression in portable lamps and in 

 reservoirs, on account of its richness in light under a little 

 volume. 



As light only is wanted, we are not forced, as with coal 

 gas, to create at the same time disagreeable residues, and ac- 

 cessory products, which would be gladly dispensed with ; but 

 on the more or less advantageous sale of which depends, ne- 

 vertheless, the profit or loss of the undertaking ; in short, in 

 distilling oil, gas only is obtained. 



The rise or fall of oils is moreover nearly indifferent to the 

 manufacturer who knows how to produce good gas with raw 

 oils of the most inferior qualities, such as will cost him, for ex- 

 ample, forty-seven francs the hectolitre; whilst the consumer, 

 to supply Argand lamps, must buy purified oil, perhaps at the 

 rate of fifty-seven francs ; besides that the light of an oil lamp 

 is necessarily influenced- by a number of circumstances more 

 or less favourable : as by the length and uniform height of 

 the wick ; by the fineness of the fibres of the cotton of which 

 it is composed, and which help the capillary attraction ; by its 

 dryness, for it is a body sensibly hygrometric, and if it has 

 become charged with humidity from the air, it is thereby less 

 fit to imbibe the oil ; by its state of carbonization more or less 

 advanced ; by the actual level of the oil, always lowering (ex- 

 cept in the beautiful lamp of Carcel) ; by the quality of the 

 oil itself, and by the processes of purification it has under- 

 gone; lastl}', by the more or less care with which the Argand 

 lamp has been daily cleaned, &c. ; not to speak of the form of 

 glasses and other circumstances which modify generally the 

 effect of the various kinds of lights, without excepting gas. 



Although these details may appear very trifling, they are 

 notwithstanding, without exception, of such importance, that 

 if there is a disproportion in one single {)oinl, the light of the 

 Argand lamp must necessarily be imperfect; it is seen for this 

 same reason how much this mode of ligliting is subject to 

 chance. I will say more : it is on the coincidence of all these nice 

 points, with a just proportion of dry ambient air flowing in with 

 a constant and regular speed, tluit the temperature depends at 

 which the decomposition of the oil anil the consequent com- 

 bustion of the gas is effected. In short, if the temperature is 

 too low, a portion of oil escapes, eitlier under the Ibrm of oily 

 vapour, or under that of smoke, without being burnt : if on 



the 



