ARGON, A NEW CONSTITUENT OF THE ATMOSPHERE. 43 



elements which miglit be expected to follow fluorine in the periodic table. Such 

 elements should have atomic weights between IS), the atomic weight of fluorine, 

 and 23, the atomic weight of sodium. But this view is completely put out of 

 court by the discovery of the moiiatomic nature of its molecules. We are therefore 

 led to look for a gap for an element of atomic weight 40. The series in this neigh" 

 boiliood is : Chloi'ine 35.5 ; a possible trio of elements with atomic weights between 

 that of chlorine and that of })otassium ; potassium 39 ; calcium 40 ; scandium 44. 

 There can be no doubt that potassium, calcium, and scandium follow legitimately 

 their predecessors in the vertical columns, lithium, beryllium, and boron ; and 

 that they are in almost certain relation with rubidium, strontium, and (l)ut not 

 so certainly) yttrium. If argon be a single element then there is reason to 

 doubt whether the pei'iodic classification of the elements is complete ; whether, in 

 fact, elements do not exist which cannot be fitted among those of which it is 

 com[)osed. On the other hand, if argon be a mixture of two elements they might 

 find place in the eighth group ; one after chlorine, and the other after bromine. 

 Necessarily the last must needs be present in very small proportion. 



In conclusion, it need excite no astonishment that argon is so indifferent to 

 i-eagents. For mercury, although a monatomic element, forms compounds which 

 are by no means stable at a high temperature in the gaseous state ; and as for the 

 physical condition of argon, that of a gas, we possess no knowledge why carbon, 

 with its low atomic weight, should be a solid, while nitrogen is a gas, except in so 

 far as we ascribe molecular complexity to the former, and comparative molecular 

 simplicity to the latter. Argon, with its comparatively low atomic weight, and its 

 molecular simplicity, might well be expected to rank among the gases. And its 

 inertness, which has suggested its name, sufficiently explains why it has not pre- 

 viously been discovered among compound bodies. 



We would suggest for this gas, assuming provisionally that it is not a mixture, 

 the symbol A. 



