1820.] the Atoms of Barytes, Potash, Soda, S)C. 335 



two portions. Into one portion drop a little nitrate of lead ; 

 into the other a little sulphate of soda. The liquid will not be 

 affected by either of these reagents. Hence it. is obvious that it 

 contains no sulphuric acid, and no oxide of lead. Consequently 

 the two salts when mixed in the proportions above indicated 

 exactly decompose each other. We see that sulphate of lead is 

 composed of 



Sulphuric acid 5 



Protoxide of lead 14 



And nitrate of potash of 



Nitric acid 6-75 



Potash 6-00 



12-75 



If we talce the proportions indicated by Berzehus, the hquid 

 will contain an excess of sulphuric acid. Dr. Wollaston's pro- 

 portions will leave an excess of oxide of lead. It is obvious then 

 that the weight of an atom of lead is 13, and the weight of an 

 atom of protoxide of lead 14. Consequently all the analyses 

 which Berzelius has made by means of salts of lead are somewhat 

 inaccurate. The degree of error may be easily estimated from 

 what has been said above. 



The only remaining atomic w^eight in the little table given 

 near the beginning of this essay which requires to be verified is 

 that of chromic acid. In a preceding paper I have described 

 the methods which I employed to prepare chromate and bichro- 

 mate of potash ; but I have reserved for this place a detail of the 

 experiments by means of which the true weight of an atom of 

 chromic acid and the true composition of the chroraates was 

 ascertained. The only person who has attempted before me to 

 determine the weight of this acid is Prof. Berzelius ; his number 

 when reduced by dividing by 2 is 6\5182, which is only a very 

 little greater than 6*3, the number which I pitched upon in con- 

 sequence of the near approach of Berzelius's number to that 

 quantity. 6"5182 is not only a number difficult to remember, 

 but it is not a multiple of 0"12o ; whereas 6*5 is obviously a mul- 

 tiple ; for 0-125 X 52 = 6-o. 



Bichromate of potash is a compound of two atoms chroiiiic 

 acid and one atom potash. 



2 atoms chromic acid , . . = 13 



1 atom potash = 6 



19 



Chromate of lead is a compound of 



