202 SCIENTIFIC APPARATUS. 



all the elementary bodies are constituted of minute indivisible 

 particles or atoms, and that compounds are formed by the union 

 of these atoms. He was led to this idea by the examination of 

 two compounds of carbon and hydrogen called olefiant gas and 

 marsh gas, when he found that the latter gas contained, for the 

 same amount of carbon, exactly twice as much hydrogen as the 

 former; he therefore supposed that olefiant gas- was composed of 

 one atom of carbon united with one atom of hydrogen, whilst 

 marsh gas contained one atom of carbon united with two atoms 

 of hydrogen. An interesting collection of apparatus used by 

 Dalton, much of which was made with his own hands, is 

 contributed by the Literary and Philosophical Society of Man- 

 chester. In 1808 Gay-Lussac showed that when gases com- 

 bine there is a very simple relation between the volumes of the 

 constituents and the volume of the product when measured in the 

 form of gas or vapour. Thus, two volumes of hydrogen combine 

 with one volume of oxygen to form two volumes of steam, and two 

 volumes of ammonia consist of one volume of nitrogen united to 

 three volumes of hydrogen. These singularities are now explained 

 by the dynamical theory of gases, which leads to the conclusion 

 that equal volumes of different gases contain equal numbers of 

 molecules. These molecules may be simple or compound, con- 

 sisting of one elementary atom, or of a number of such atoms. 



The constitution of matter has been much elucidated by the 

 study of organic compounds. These are bodies derived from the 

 vegetable and animal kingdoms. Many of them have been long 

 known, but it was not until 1811 that precise analyses of organic 

 bodies were attempted, by Gay-Lussac and Thenard; the pro- 

 cesses were afterwards modified by Berzelius, De Saussure, and 

 Prout, and finally brought to perfection by the investigations of 

 Liebig. 



The atomic theory was much advanced by the discovery, in 

 1815, by Gay-Lussac, of cyanogen, a gaseous compound of carbon 

 and nitrogen, possessing many properties analogous to those of the 



