CHEMISTRY. 189 



into contact with the mixture, explosion results. Now this point, 

 the point to which the petroleum must be raised in temperature 

 before its vapor is emitted rapidly enough to form, an explosive 

 mixture with the air in the vicinity, will of course vary according 

 to the quality of the petroleum, will vary with the proportion of 

 " spirit" removed by the refiner. If enough has been boiled off, 

 the oil is perfectly safe ; but, unfortunately, it is not to the interest 

 of all parties to remove the spirit ; hence much of the petroleum 

 sold in retail shops is dangerous to use. Should a lamp fed with 

 it become a little warmer than usual, an explosive mixture forms 

 in the chamber of the lamp, and any flame brought accidentally 

 or thoughtlessly into contact with the mixture, gives rise to explo- 

 sion. Hence the legislature of this country has wisely ordered 

 that large quantities of crude petroleum shall not be stored within 

 fifty yards of a dwelling-house or warehouse except under license; 

 and the act states that " Petroleum shall include any product 

 thereof that gives off an inflammable vapor at a temperature of 

 less than 100 of Fahrenheit's thermometer." That is to say, re- 

 fined petroleum, such as is commonly vended in retail shops as 

 * Crystal Oil," " Photogen," ' American Paraffine Oil," etc., etc., 

 for illuminating purposes, must not be kept in or near a house in 

 larger quantities than 40 gallons, unless proof is forthcoming 

 that it dues not give off inflammable vapor below 100 F. If it 

 will stand this test, then the liquid is not petroleum within the 

 meaning of the act, and the owner of it runs no risk. 



The ordinary methods of ascertaining the point of ignition are 

 uncertain, and therefore not safe. The time employed in the 

 operation of taking the point, as usually practised, is the first 

 cause of variation. That is to say, if the petroleum be rapidly 

 raised in temperature, it will explode at a lower heat than if it bo 

 raised slowly. The rate of escape of vapor, as produced by agi- 

 tation, will also promote explosion, because more is given off in a 

 given time than when the fluid is quiet. The shape of the vessel 

 also makes a difference. Thus in a bottle the explosion will take 

 place, other things being equal, at a lower temperature than in an 

 open dish. The arrangement of the vessel over the source of 

 heat makes a difference ; the distance of the test-flame from the 

 petroleum, and the amount of petroleum operated on. 



These, then, are causes, amply sufficient in number and nature, 

 of the variation in the igniting-point of petroleum, as observed by 

 different experimenters, or Toy the same experimenter at different 

 times. They fully explain the fact that I have found a specimen 

 of petroleum to ignite at almost any degree between 78 F. and 

 124 F. Before proceeding to suggest a modified method of ob- 

 servation which shall give constant results, it may be instructive 

 to-give a table of the igniting-points of several specimens of re- 

 fined petroleum recently circulating in wholesale and retail com- 

 merce, the experiment on each specimen being taken under three 

 conditions : first, heating in an open earthenware bowl ; second, 

 heating in a two-ounce, wide-mouth, white glass phial, without 

 shaking the petroleum ; and third, as the second, except that be- 

 fore introducing the test-flaine the stopper was inserted in the bot- 



