1818.] the Commencement of the Year 1817. Parti. 3 



attempted to determine the expansibility of bodies by heat. 

 The object of the important experiments of Dulong and Petit 

 was to determine with as much precision as possible the rate of 

 the expansion of different bodies, in order to ascertain how far 

 the peculiar opinions of Mr. Dalton are well founded : the analysis 

 of this paper will be given in a subsequent number. 



3. Sir Humphry Davy's researches on flame are distinguished 

 by that analytical skill and that inventive genius which so 

 eminently characterize the investigations of this sagacious philo- 

 sopher, to whom chemistry lies under so many and so important 

 obligations. These researches have been detailed at such length 

 in the preceding volumes of the Annals of Philocophy, that it is 

 unnecessary to enter here into minute details. Flame he con- 

 ceives to be aerial matter heated so high as to be luminous. And 

 it would appear that different temperatures are necessary to 

 maintain the combustion of different gaseous bodies. When 

 we cool them below that temperature, they can burn no longer, 

 and of course are extinguished. Hence the reason why a 

 covering of wire gauze prevents a lamp from exploding the car- 

 bureted hydrogen gas in coal mines, even when it is mixed with 

 such a proportion of common air as to be at the exploding point. 

 The heat is so much diminished by the wire, that the aerial 

 matter which passes through is too cold to be capable of setting 

 fire to the coal gas. When a hot platinum wire of a small 

 diameter is put into an exploding mixture of a combustible gas, 

 it becomes red hot, and continues luminous for a long time, a 

 combustion of the gas going on around the wire, evolving suffi- 

 cient heat to maintain the luminous temperature of the wire ; 

 but insufficient to explode the gaseous mixture. This very 

 curious and important fact has been applied to # the maintaining 

 what is called a lamp without flame. A few coils of platinum 

 wire, about -p^th of an inch in diameter, are placed around the 

 wick of a spirit lamp. The lamp after burning a short time is 

 blown out, and the platinum wire becomes luminous, and conti- 

 nues so till the whole of the alcohol in the lamp is consumed* 

 Platinum has the smallest specific heat, and is the worst con- 

 ductor of heat of any of the metals that can be drawn out into 

 wire. Hence probably the reason why it is the only metal that 

 answers for these experiments. Platinum possesses also another 

 property which seems to be peculiar to it. Its specific heat is 

 not sensibly increased by elevating its temperature. At least 

 Dulong and Petit found that the specific heat of platinum, raised 

 to the temperature of 572°, was no greater than that of platinum 

 simply heated to 212°. 



4. Animal Heat. — The curious experiments of Mr. Brodie 

 upon rabbits will be recollected by all our readers. He deca- 

 pitated these animals, but kept up their respiration by artificial 

 means. The air underwent the usual changes, but the tempera- 



• Annuls of Philosophy, xi. 217, 004, 306, aud 43T. 

 A 2 



