238 



PROGRESS IN CHEMISTRY. 



two of hydrogen, and similarl}' for the two oxides of carbon. Know- 

 ing the relative weights in which these elements enter into combination, 

 we can deduce the relative weights of the atoms. Placing the relative 

 weight of an atom of hydrogen equal to unity, we have: 



Thus the first compound, marsh gas, was regarded ))y Dalton as com- 

 posed of an atom of carbon in union with an atom of hydrogen; or. to 

 reproduce his sj^mbols, as #©, while the second, olefiant gas, on this 

 hypothesis, was a compound of two atoms of hydrogen with one of 

 carbon, or 0#0. Similarly the symbols #0 and 0#0 were given 

 to the two compounds of carbon with oxygen. So water was assigned 

 the symbol OO, for Dalton imagined it to be a compound of one atom 

 of hydrogen with one of oxygen. Compounds containing only two 

 atoms were termed by him '''binary;'' those containing three, ''ter- 

 nary;" four, "quaternary,'* and so on. The weight of an atom of 

 oxygen was eight times that of an atom of hydrogen, while that of an 

 atom of carbon was six times as great as the luiit. By assigning sym- 

 bols to the elements, consisting of the initial letters of their names, or 

 of the first two letters, formuhe were developed, indicating the com- 

 position of the compound, the atomic weights of the elements ))eing 

 assured. Thus, NaO signified a compound of an atom of sodium 

 (natrium) weighing twenty-three times as much as a similar atom of 

 hydrogen with an atom of oxygen possessing eight times the weight 

 of an atom of h3'drogen. Therefore, 81 pounds of soda should consist 

 of 28 pounds of sodium in combination with 8 pounds of oxygen, for, 

 according to Dalton, each smallest particle of soda contains an atom of 

 each element, and the proportion is not changed however many particles 

 may be considered. 



It has been pointed out by Judge Stallo, of Philadelphia, in his Con- 

 cepts of Physics that such an hypothesis as that of Dalton is no 

 explanation; that a fact of nature, as, for example, the fact of simple 

 and nmltiple proportions, is not explained b}" being minified. Allow- 

 ing the general truth of this statement, it is nevertheless undoubted 

 that chemistry owes nuich to Dalton's hypothesis; a lucky guess at first, 

 it represents one of the fundamental truths of nature, although its 

 form must be somewhat modified from that in which Dalton conceived 

 it. Dalton's work was first expounded })y Thomas Thomson, pro- 

 fessor at Glasgow, in his System of Chemistry, published in 1805, 

 and subsequently in Dalton's own New System of Chemical Philos- 

 ophy, the three volumes of which were published in 1808, in 1810, 

 and in 1827. 



