14 Historical Sketch of Improvements in [July, 



states it. Davy attempted to alloy together tellurium and 

 potassium. A good deal of heat was disengaged, and a gas was 

 evolved which could not be condensed, and which broke the 

 apparatus to pieces.— (Journ. de Pharm. v. 505.) 



5_ Tron. — Mr. Porrett has been led by the constitution of 

 ferrochyazic acid, as determined by his experiments, and my own, 

 to consider the weight of an atom of iron to be only 1-75, or half 

 the number which I have assigned in the last edition of my 

 System of Chemistry. I think it by no means unlikely that the 

 opinion is well founded ; though I am unwiUing to introduce this 

 new weio"ht into the atomic theory till we have made further 

 progress in our knowledge of the laws that substances observe 

 with respect to their combinations. Mr. Porrett has given us 

 the following table of the combinations of iron and sulphur, 

 which he considers as highly favourable to his view of the 

 subject : 



1. Cubic Pyrites. 



1 atom iron = 1*75 



1 atom sulphur = 2*00 



3-75 

 2. Magnetic Pyrites. 



2 atoms iron = 3-5 



1 atom sulphur «= 2-0 



3. Sesquisulphuret. 



3 atoms iron = 5*25 



2 atoms sulphur = 4*00 



?25 



4. Tritosulphuret . 



4 atoms iron = 7 



3 atoms sulphur = 6 



13 



The last two of these sulphurets Mr. Porrett informs us were 

 formed by Proust, and described by him in his paper on the 

 Native and Artificial Sulphurets of Iron ; but it does not appear 

 from his paper that Proust was aware of any other sulphurets of 

 iron, except magnetic and cubic pyrites. 



M. Duleau has pubhshed a set of experiments on the force of 

 malleable iron to resist being crushed when placed in a vertical 

 situation, or when constituting a part of a vault. The following 

 propositions contain the most important consequences which he 

 nas deduced from his experiments : 



For two rectangular pieces of different sizes charged perpendi- 

 cularly to their length, the bendings, or the descents, of the 



