1820.] Chromate and Bichromate of Iron. 327 



13 acid + 6 potash. Thus the weight of potash in each being 

 the same, the weight of acid in the bichromate is precisely 

 double that in the chromate. The analysis of the bichromate is 

 much easier than that of the chromate, because it is easy to 

 procure the salt pure. 



Article IT. 



Experiments to determine the true Weight of the Atoms of 

 Barytes, Potash, Soda, Lead, Sulphuric Acid, Nitric Acid, 

 Muriatic Acid, and Chromic Acid. By Thomas Thomson^ 

 M.D. F.R.S. 



In my paper on the Specific Gravity of the Gases, inserted in 

 the last number of the Annals of Philosophy, p. 241, I stated 

 that it was impossible for Prof. Berzelius ever to deduce the true 

 composition of sulphuric acid from his analysis of the sulphates, 

 because the numbers which he assigns to the constituents of 

 sulphate of barytes, by means of which all his analyses are calcu- 

 lated, are not quite accurate. I am aware that in consequence 

 of the high character which Berzelius bears for precision, and 

 which he in fact so richly deserves, such an allegation on my 

 part will not, and indeed ought not, to be admitted unless its 

 truth be demonstrated by experiments of the most decisive 

 nature. 1 consider it as necessary, therefore, to lay before my 

 readers the reasons upon which my opinions are founded with as 

 little delay as possible ; and I have no doubt that after I have 

 stated them, and after the experiments have been repeated and 

 confirmed by others, as they undoubtedly Lvill be, every practical 

 chemist, who turns his attention to the subject, and even Berze- 

 lius himself, will admit that the numbers, or at least the ratios, 

 which I shall assign to the weights of the atoms of the sub- 

 stances enumerated at the head of this essay are mathematically 

 accurate, or at least that the error, if any exist, is wholly unap- 

 preciable. 



That chemists are still far from being agreed about the atomic 

 w-eights of these important bodies must be well known to every 

 person at all interested in the subject. Determinations of them 

 have been published by Dalton, Wollaston, Berzelius, and 

 myself, and perhaps also by others whose results I do not at 

 present recollect. The following little table exhibits the weights 

 of the respective atoms according to these various chemists. To 

 enable the reader to compare them together, I have reduced 

 them to what they would be on the supposition that the weight 

 of an atom of oxygen is unity ; because this is the mode which I 

 myself am accustomed to employ. 



