1819.] and on the Atomic Weight for Iron. 301 



exactly contains this increase of sulphur over that in the proto- 

 sulphuret. Proust's experiments give the proportions of sulphur 

 in these two sulphurets as 60 to 90 with 100 of the metal, 

 numbers which differ but little from those in the table. 



It is, therefore, evident, from the two experiments just de- 

 scribed, that Proust had formed two new compounds, the deuto 

 and the tritosulphurets, although he was not himself aware of it, 

 but considered them as agreeing in composition with the two 

 sulphurets commonly known as protosulphuret and as persul- 

 phuret. 



From the preceding experiments and deductions, I think it 

 will be clear that the atom of oxygen being 10, that of iron 

 should be represented by the number 17-5, the same as that of 

 azote, and that we are now entitled to consider the atomofferro- 

 chyazic acid as composed of 



4 atoms of carbon = 30*00 



1 atom of azote = 17-50 



1 atom of iron = 17-50 



1 atom of hydrogen = 1*25 



66-25 



also that this acid combines with one atom of base and two 

 atoms of water to form the ferro-chyazates. 



The reduced weight for an atom of iron will, I trust, account 

 for the small proportion in which this metal and its oxides enter 

 into the composition of several mineral bodies, and will, perhaps, 

 show that in some of those instances where it has been consi- 

 dered as an accidental ingredient, it is in reality chemically 

 united in atomic proportions with the other constituents of the 

 mineral. 



Toicer, Sept. 18, 1819. 



Article XI. 

 Analyses of Books. 



A Critical Examination of tliejirst Principles of Geology; in a 

 Series of Essays. By G. B. Greenough, President of the 

 Geological Society, F.R.S. F.L.S. London. 



This work deserves the particular attention of geologists. It 

 comes from a gentleman who has been for many years enthusi- 

 astically devoted to geological pursuits ; who has dedicated to 

 them the greatest part of his time and study, and who has 

 appropriated a very handsome fortune to the promotion of his 

 favourite objects. He has read every thing that has been writ- 



