1824.] Power of Bodies to conduct Electricity. 41 



ties, the strongest analogies to that substance. For instance, 

 every thing being equal in both cases, olive oil required forty 

 minutes to produce a certain deviation, while poppy oil, or the 

 oil of the beech-mast, required only twenty-seven seconds to 

 produce the same deviation. One-hundredth part of any other 

 oil added to oil of olives reduces the time to ten minutes. It 

 would, therefore, be easy to discover by means of this instru- 

 ment the smallest traces of any oil fraudulently mixed with oil of 

 olives. 



If the proportion of the foreign substance be considerable, the 

 difference of time necessary to produce the maximum of effect 

 would no longer be sufficiently great, and could not be measured 

 with sufficient precision to indicate the proportion of the 

 elements ; but the apparatus might easily be modified so as to 

 adapt it to this kind of determination. 



The solid fats are worse conductors than the animal oils, aris- 

 ing no doubt from the large proportion of stearine contained in 

 the former; for M. Rousseau is satisfied, by comparative trials 

 with stearine and elaine, prepared by M. Chevreul, that the 

 conducting power of the latter much exceeds that of the former. 

 The fat of an animal becomes a worse conductor in proportion 

 to the age of the individual which afforded it. 



By means of the same apparatus, we may also observe a nota- 

 ble difference between resin, gum lac, and sulphur, the most 

 insulating of all known substances, and silk, crystal, and com- 

 mon glass. 



M. Rousseau has not found any difference in the conducting 

 power of liquids, whether spirituous or aqueous, acid, alkaline or 

 neuter, the time required by the needle to arrive at the maximum 

 of deviation being too short, in every case, to ascertain the 

 inequality of its duration. But a modification of the apparatus, 

 similar to that for determining the proportions in an oleaginous 

 mixture, would easily appreciate that difference. 



It would be equally possible, and very curious, to try the 

 effect of the two kinds of electricity on different substances ; all 

 that would be necessary would be to place the two poles alter- 

 nately in connexion with the ground. According to Ermann's 

 results, it is probable that a difference would be found between 

 some substances. 



