342 Dr. Thomson's Observations on the Weights of [Nov. 



Weight of an atom, 



13 Potassium 5-000 



14 Sodium 3-000 



15 Calcium : 2*625 



16 Barium 8-750 



17 Strontium 5*500 



18 Magnesium 1-500 s 



19 Potash 6-000 h 



20 Soda 4-000 ■ 



difficulty than those upon other metals. The number 4-75 

 results from the compounds which arsenic forms with oxygen ; 

 but it does not agree well with the chloride of arsenic. Besides, 

 if 4-75 be the weight of an atom of arsenic, neither arsenious nor 

 arsenic acid will contain whole atoms of oxygen ; for the first 

 will be a compound of 1 atom arsenic + 14- atom oxygen, and 

 the second of 1 atom arsenic + 2-±- atoms oxygen. These ano- 

 malies render it very unlikely that an atom of arsenic really 

 weighs 4-75. 



g But few changes have been made upon the weights of the 

 atoms of these six alkaline metals. The supposition that an 

 atom of sodium weighs three, tallies very well with experiments, 

 if we suppose soda to be a compound of 1 atom sodium + 1 atom 

 oxygen. On that supposition soda will weigh 4, which agrees 

 with the weight resulting from the composition of the salts of 

 soda. The number for strontium results from the mean of Stro- 

 meyer's analyses of the salts of strontian, and my own. The 

 number for magnesium is founded on Berzelius's analysis of 

 sulphate of magnesia. 



h This number is very convenient, and it tallies as well with 

 the analyses of the salts of potash as any other. 



Acid. Potash. 



Kirwan found sulphate of potash composed of. . 45-20 + 54'80 



Wenzel 45-30 + 54-70 



Thomson 45-72 + 54-28 



Mean 45-40 + 54-60 



If it be a compound of 5 acid + 6 potash, its 7 Ar AR r A KA 

 constituents are 5 *°" 4D + M '^ 



I consider this as almost an exact coincidence. 

 ' This number agrees equally well for soda. 



Water. Acid. Soda. 



Berzelius found sulphate of soda com- 7 r ■ <-m -a m oa 



posed of. I 56 + 24 - /6+ 19 ' 24 



If it contains 5 acid + 4 soda, its con- 7 ra , ca ap, , ir> rn 



stituents will be X 56 + 24 ' 40 + 19 ' 60 



