OlS" KEROSENE OIL. 79 



to be alight or a, dense oil; those known as light being regarded 

 dangerous, while the heavy oils are called safe. But the specific 

 gravity of kerosene, as shown below, is not an invariable indica- 

 tion of its purity. 



Soon after the introduction of kerosene as a burning fluid, a 

 method called the " fire-test " was devised for the detection of dan- 

 gerous oils. It consists in determining the temperature at which 

 an inflamable vapor is evolved, or the "flashing point;" and also 

 the temperature at which the fluid becomes ignited from the flash 

 of the vapor and continues to burn, or the " burning point." The 

 flashing point is determined by inserting the bulb of a thermome- 

 ter half an inch below the surface of the fluid to be tested, and 

 gradually raising the temperature from sixty or seventy degrees, to 

 the point at which a ]3ale blue flicker is observed to pass across the 

 surface upon the approach of a small flame or lighted match. The 

 burning point is usually from ten to fifteen degrees above the 

 flashing point. 



If an oil gives off a combustible vapor, or flashes, at a low tem- 

 perature, there is danger of forming a very explosive mixture with 

 about four volumes of atmospheric air, especially in a confined 

 space. This mixture is often formed in a kerosene lamp, contain- 

 ing a small quantity of oil, in attempting to refill it while still 

 burning. It is also formed if the temperature of a partially filled 

 lamp is suddenly lowered by changing it from a warm to a cool 

 room, or by allowing a cold draught of air to come in contact with 

 it. In these cases a part of the vapor above the oil condenses, air 

 rushes in to fill the partial vacuum, the flame has a tendency to 

 descend and an explosion is apt to take place. The oil itself never 

 explodes, it is a mixture of vapor and atmospheric air that bursts 

 the lamp and kindles the flame, hence the necessity of keeping 

 lamps well filled and uniform temperatures. 



Laws have been enacted by several State legislatures, and a spec- 

 ial act was passed by congress March 2, 1867, which however, has 

 since been declared unconstitutional, fixing the temperature at 

 which hydro-carbon oil may be deemed safe and merchantable, at 

 not less than one hundred degrees Fahrenheit, for the flashing 

 point, nor below one hundred and ten degrees Fahrenheit for the 

 burning point. An oil which will stand these tests may be regard- 

 ed as perfectly safe. The results of my observations show that 



