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At the last meeting of the French Academy of Sciences, the following communication was presented by M, Dumas, from M. Maumene, on the above subject. The fatty oils mingled with sulphuric acid disengage heat, this action may serve to distinguish them; it separates in a striking manner the drying oils from those that are not so. Fifty grammes of olive oil having been placed in an ordinary test glass, the temperature of which was known by plunging a thermometer in the liquor, there were carefully dropped into it 10 cubic centimetres of sulphuric acid at the temperature of 66 (Baume). While mixing the liquids the thermometer was shaken, and the rise of tke mercury noted. Beginning with the temperature of 25 for the oil and acid, the thermometer rose to 67—increase, 42. The mix- ing does not take more than two minutes, only one minute is required to obtain the maximum temperature. In another similar glass there were placed 50 grammes of oil of poppies, and it was likewise tested with sulphuric acid, the thermometer rose from 26 to 100'5—increase, 74 '5. In this instance there was noticed, firstly, a very remarkable developement of sulphurous acid, not caused by olive oil; and, secondly, a very great bubbling up of the liquid. On account of these two circumstances, the figure 740*5 is too small. The difference between 42 and 74“'5 is sufficiently great to present a mode of analysis. The experiment repeated several times under the same conditions, with the same olive oil, gave each time the same developement of heat at 42. The experiment made with different sorts of olive oil, from various sources, proved that Hie action of the sulphuric acid is constant when the oil is pure, and when made oil of ben and of tar cannot be mixed with olive oil, consequently, whenever olive oil gives more than 42 of heat in its mixture with 10 cubic centimetres of sulphuric acid (at 25) their oil is not pure. The preceding appears sufficient to show the use that may be made of sulphuric acid for analyzing oils. In mixtures composed only of two oils, the employment of this acid will very much help in determining its quality. When the qualitative analysis has been made the quantity may often be declared with precision.
