Daltons Atomic Theory. 35$ 



Two factors determine every great advance in science — a 

 fact, and a mind prepared for the full and complete appre- 

 ciation of the fact. Moreover, the fact must be at hand when 

 it is wanted by the mind. These conditions were satisfied 

 when Galileo observed the oscillating lamp in the Cathedral 

 of Pisa ; when Newton saw the falling apple ; when Malus 

 observed the ray reflected from the window of the Luxem- 

 bourg ; when Lavoisier was informed of the discovery of 

 oxygen by Scheele and Priestley (D. 20-21). 



The discovery of oxygen is the great fact with which the 

 history of scientific chemistry commences ; but neither of the 

 discoverers — neither Priestley nor Scheele — recognized the 

 significance of the discovery. Lavoisier's mind was the good 

 soil wherein the seed bore fruit, because it was well prepared 

 by a careful repetition of the experiments of Black and Meyer. 

 These experiments prove that carbonates are combinations of 

 a gas which can be transferred from one base to another* 

 Quicklime absorbs carbonic acid from the atmosphere and 

 turns into carbonate of lime. These facts raised in Lavoisier's 

 mind the question : Do metals absorb a gas from the atmo- 

 sphere during calcination ? The answer from his own expe- 

 riments was a decided " Yes." But as he could not prepare 

 the gas absorbed, the investigation could not proceed. Then, 

 just at the right moment, Scheele and Priestley informed 

 Lavoisier of the discovery of oxygen, and the antiphlogistic 

 chemistry was born (D. 21). 



Dalton, the meteorologist, wished to determine the compo- 

 sition of the atmosphere. For this purpose he tried the 

 absorption of oxygen with nitric oxide. In his note-book 

 occurs the following memorandum, dated August 4th, 1803: — 



" It appears, too, that a very rapid mixture of equal parts 

 of common air and nitric oxide give 112 or 120 residuum. 

 Consequently i that oxygen joins to nitric oxide sometimes 

 1-7 : 1 or at other times 3*4 : 1 » (R. 38, Al. 8). 



In the Essay on the Composition of the Atmosphere occurs 

 the remark, " These facts clearly point to the theory of the 

 process ; the elements of oxygen may combine with a certain 

 portion of nitric oxide, or with twice that portion, but with no 

 intermediate quantity " (R. 33, Al. 9). 



A month after the date of the above note, on September 6th, 

 1803, the note-book contains a list of atomic weights (R. 29) , 

 and on the 19th of the same month the diameters of the 

 molecules of a certain number of gases were written down 

 (R.41). 



May we venture to conclude, on the strength of these facts, 

 that the observations of the proportions in which nitric oxide 

 and oxygen combine over water originated in Dalton's mind 



