Polytechnic Association Proceedings. 745 



coveiy made many years ago by M. Rousseau, of France, that 

 olive oil — the feeblest conductor of electricity — when mixed with 

 one hundredth of its volume of oil of poppies increased the num- 

 ber of vibrations of a magnetic needle in a given time, when the 

 same was included or made to form a part of a voltaic current. 

 He gives a table of resistances of volatile and fixed oils, and 

 remarks that the adulterants of volatile oils are principall}'- tur- 

 pentine and alcohol. Compared with any of the essential oils, 

 turpentine has an immense resistance, while that of alcohol is 

 enormously lower than any of them, except, perhaps, that of the 

 oil of bitter almonds, which was so low that he did not measure it 

 in any of his experiments. The importance of this general fact is 

 at once apparent, since the addition either of alcohol or turpentine 

 in the smallest quantity is readily detected; and the quantity is 

 denoted by the variation in the deflector, either when compared 

 with a standard of known purity or by the resistances themselves. 

 The oils of lemon and bergamot, when mixed with a small propor- 

 tion of turpentine, do not, however, show such marked diflerences 

 as the generality of essential oils. The efiects produced by mixing 

 different specimens of the same oil together are also perceptible; 

 th\is the German oils of peppermint or foreign samples of lavender 

 oil produce modifications on the electrolysis. The resistances of 

 the volatile oils were determined in these experiments by the use 

 of one cell, but for testing fixed oils thirty-two cells were used. 

 The author found that bleached fixed oils possessed a lower con- 

 ducting power than unbleached oils, and the difference was very 

 great in the case of olive oil. A singular difference existed between 

 the Italian and East Indian castor oils, which was so wide that a 

 very small percentage of one added to the other could be detected. 

 Cotton-seed oil and oil of poppy, as well as turpentine, are so 

 rapidly altered in their conducting power by electrolysis, that there 

 is not the slightest difficulty in recognizing them in samples of oil. 

 Olive oil, when free from-cotton seed oil or oil of poppy, has its 

 resistance increased by electrification; but if the smallest quantity 

 of either of them exists in a sample of olive oil, it produces a con- 

 trary effect, by a prolonged contact with the battery. The author 

 of this paper has not, however, proposed any plan for testing oils 

 which can be made of practical use in commercial transactions. 

 The purity of oils cannot be ascertained readily by this or any 

 other plan thus far proposed. An instrument for this purpose, 

 adapted to the use of oil merchants, is now a great desideratum. 



