1830.] The Progress of Physical Discovery. 25 



binations directly opposite are produced. And these results are of great 

 moment, inasmuch as nothing can more strongly refute the old theory 

 of Bergman, or confirm the principle laid down by Berthollet, of the 

 influence of the mass of substances in chemical phenomena, and that 

 there is no such thing as absolute elective affinity. 



The year 1812 was signalized by the great additions made by Count 

 Rumford to our knowledge of the sources of heat. His main idea was 

 to measure the quantity of water that passes from a fixed degree to 

 another, also fixed by the combustion of a given quantity of each sub- 

 stance. In applying this process to the determination of the quantity 

 of heat developed by the combustion of different kinds of wood, he 

 arrived at the singular result that the specific weight of the solid matter 

 which forms the timber of wood is nearly the same in all trees ; and that 

 the ligneous part in the oak in full vegetation only forms four-tenths of 

 the whole ; the air being one-fourth, and the root being composed of 

 sap. Dry wood contains, in general, water equal to one-fourth of its 

 weight, and even in timbers a century old there is not less than a tenth 

 of water. Count Rumford has concluded that the peculiar matter of 

 wood is identical in all trees, and that there exists round the carbonic 

 fibre, or the skeleton of the wood, another substance, which may be 

 compared to the muscles, and which he calls vegetable flesh. It is this 

 substance that fire first attacks, because it contains hydrogen, which 

 makes it inflammable, and which contributes mainly to the heat yielded 

 by each wood. It would be impossible to particularize the many new 

 facts ascertained in the course of these experiments by this great che- 

 mist ; but amongst them may be mentioned that of the capability of 

 carbon to unite with oxygen, and form with it carbonic acid of a tempe- 

 rature much lower than that where it burns visibly. In respect of the 

 greatest possible produceable intensity of heat, he has established that 

 the temperature of water, at the instant when it is formed by the combi- 

 nation of oxygen and hydrogen, is eight times higher than that of red-hot 

 iron, and that the capacity of steam for heat diminishes together with its 

 temperature. 



The prize offered this year by the French Institute for the determina- 

 tion of the capacity of oxygen gas, carbonic acid, and hydrogen for heat, 

 was awarded to MM. Delaroche and Berard, whose tables are still 

 undoubted authority. M. de Saissy of Lyons, soon after, ascertained 

 that aeriform fluids have only the property of disengaging light by 

 compression when they contain oxygen gas free or weakly combined ; a 

 fact which throws additional probability on the side of the opinion, that 

 heat and light are distinct substances. Lampadius, in distilling martial 

 pyrites with carbon, had obtained a liquid and volatile substance, whose 

 nature had been hitherto doubtful; the German chemist, as well as 

 A. Berthollet, had considered it as composed of sulphur and hydrogen ; 

 and Clement and Desormes, as a combination of sulphur and charcoal. 

 M. Thenard now ascertained that it was composed of 85 per cent, of 

 sulphur, and 15 per cent, of carbon, without either nitrogen or hydro- 

 gen. Vauquelin's observations on vegetable principles are also valuable, 

 particularly his remark that acrid and caustic vegetable substances are 

 oily or resinous, and do not contain any developed acid, in which they 

 resemble poisonous plants ; whence he concludes that we ought to be 

 cautious in using any plants which do not contain acid. 



In 1813 Professor Leslie brought to still greater perfection the freezing 

 M. M. New Series. VOL. IX. No. 49. E 



