ATOMIC WEIGHTS 11 



THE FUNDAMENTAL EATIOS. 



In the determination of atomic weights, a small number of values are 

 to be regarded as fundamental. They are the standards of reference; 

 and by comparison with them all the other atomic weights are established. 

 Two of these values, the atomic weights of hydrogen and oxygen, are 

 primary; that is, one or the other of them is the basis of the entire 

 system; hydrogen as unity in the older arrangements; oxygen equal to 

 sixteen in the more modern scheme. Over the relative merits of these 

 two ultimate standards there has been much controversy; but with dis- 

 cussions of that sort the present work has nothing to do. The oxygen 

 standard is now recognized by international agreement, and will therefore 

 be accepted here. 



Comparatively few of the atomic weights, however, are fixed by direct 

 comparison with either oxygen or hydrogen. In most cases other values 

 intervene, and especially the atomic weights of silver, chlorine, bromine, 

 iodine, nitrogen, carbon, sulphur, potassium and sodium. These con- 

 stants are first to be determined, and their establishment may be com- 

 pared to a primary triangulation, of which the hydrogen-oxygen ratio 

 is the base line. The ratios connecting these eleven elements with one 

 another are to be discussed in the following pages. 



THE OXYGEN-HYDKOGEN KATIO. 



Leaving out of account the earliest researches, which now have only 

 historical interest, the first determinations of this ratio worth consider- 

 ing are those by Dulong and Berzelius,^ who, like some of their successors, 

 effected the synthesis of water over heated oxide of copper. The essential 

 features of the method are in all cases the same. Hydrogen gas is 

 passed over the hot oxide, and the water thus formed is collected and 

 weighed. From this weight and the loss of weight which the oxide under- 

 goes, the composition of water is readily calculated. Dulong and Berzelius 

 made but three experiments, which gave the following percentages of 

 oxygen and hydrogen in water: 



0. H. 



88.942 11.058 



88.809 11.191 



88.954 11.046 



^ Thomson's Annals of Philosophy, July, 1821, p. 50. 



