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500 INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 



illuminant was required. It is therefore with regret that we are urged, 

 on account of the iucreased price of the article, due in some degree to 

 the reputation as a burning material given it by the board itself, to sub- 

 stitute for it a less reliable but a much more economical material. 



At the time lard-oil was introduced a series of experiments was made 

 on the comparative value of the different petroleum oils used in this 

 country. They were however all considered too dangerous to be in- 

 trusted to the ordinary keepers of the light-stations of our coast. Since 

 the date however of these investigations, improvements have been made 

 in the manufacture of these oils, by which a much greater range has been 

 obtained in the temperature at which they give off an explosive vapor. 

 During the last two years, therefore, a new series of investigations has 

 been made relative to these illuminating agents, of which we propose in 

 the succeding pages to give a brief account. 



The crude petroleums of the Pennsylvania oil region are of a greenish 

 or yellowish appearance, and have a specific gravity of 45° to 49° 

 Beaume, at a temperature of 60° Fahrenheit. Some are so volatile as 

 to evaporate rapidly at the ordinary temperature of the air, rendering it 

 dangerous to approach an open cask of crude petroleum with a flame ; 

 others are much less volatile, requiring a temperature of from 200° to 

 300° F. to vaporize them. The volatility of the hydro-carbons is inti- 

 mately connected with their specific gravity. They become heavier as 

 the volatile ingredients are driven off by heat. The inflammability of 

 the oils is also connected with their volatility and the specific gravity. 

 The light volatile oils ignite, as we have said, on the approach of a burn- 

 ing match at ordinary temperatures, while the heavier require a higher 

 temperature for ignition. The process of manufacturing these oils con- 

 sists in separating them from each other as they occur in the crude oil 

 of the springs by what is called fractional distillation ; for this purj)ose 

 the crude oil is placed in an iron still provided with a worm of the same 

 metal submerged in a tank of water for cooling it ; the still is then grad- 

 ually heated ; the first product that passes over is gaseous at ordinary 

 temperatures, and can only be condensed into a liquid form by cooling 

 the worm with ice, or by compressing the gas with an air-pump into a 

 strong receiver. After all the vapor is given off at the temperature, say 

 at 90° F., the temperature of the liquid in the still is raised, a liquid is 

 produced which exhales in vapor at a higher temperature and is of 

 greater density — and so on, a series of liquids are produced, each of 

 which requires to be heated to a higher degree before taking fire on the 

 apijroach of a lighted match — these more volatile vapors are heavier 

 than atmospheric air, and when suffered to escape from the cask con- 

 taining them in a separate state will flow along the surface of the floor 

 of a room, and reaching a distant fire-place will ignite, and burning- 

 backward to the reservoir will set fire to the oil from which they ema- 

 nated. 



Many serious accidents have occurred in this way, by the firing of a 



