508 WRITINGS OF JOSEPH HENRY. [1873 



piece of cotton cloth about 2 feet square, which had been used 

 to wipe the table on which kerosene had been spilled, was 

 crumpled up into the condition of an ordinary dish-cloth, 

 and thrown into a corner of the room. When a lighted 

 match was dropped on this, it instantly burst forth into a 

 most violent combustion. 



These experiments are important in establishing the fact 

 that oils which are commonly sold as entirely free from 

 danger are not really so. They may be safe from explosions 

 at ordinary temperatures, and in this respect are to be pre- 

 ferred to the lighter oils ; but when spread over a large sur- 

 face they burn with greater intensity, even (as I have seen,) 

 on a surface of ice. Indeed, the results are so striking, that 

 it might be well to repeat them in the presence of every 

 light-house keeper, in order to impress him with an idea of 

 the danger to be apprehended in spilling the oil over his 

 clothes, or in carelessly dropping his matches on cloths which 

 which had been used in cleaning the apparatus. 



Among the peculiar properties of mineral oil is its great 

 surface-attraction or power of adhering and spreading on 

 other surfaces, as well as ascending wicks to a much greater 

 height than other oils. This property is recognized by the 

 house-keeper who finds the exterior of the lamp covered with 

 a film of oil shortly after it has been subjected to a thorough 

 cleansing. It rises along the interior surface of the lamp 

 and spreads over the outside. On account of this property 

 it can be freely burned in lamps of which the fountain is at a 

 considerable distance below the flame, and in which no over- 

 flow is required to produce a brilliant combustion. 



A series of experiments was next made with regard to the 

 burning qualities of mineral oils of different densities, from 

 which it was inferred that the lighter oils in lamps of the 

 fourth order gave a greater amount of illumination than 

 the heavier oils, and furthermore that the latter charge the 

 wick more than the former, from which it would appear that 

 in using mineral oil, while safety should be the prominent 

 consideration on the one hand, in the choice of the material, 

 regard must be had on the other, to the illuminating power. 



