20 Historical Sketch of Improvements in [July, 



tarnished, and exhibits on the surface small quantities of oxide 

 of tin. 



When tin is alloyed with some per cents, of copper, this last 

 metal may be distinguished on the cupel by the rose-red colour 

 which makes its appearance. (Ann. de Chim. et de Phys. xii. 342.) 



VII. Acids. 



1. Boracic Acid. — The experiments of Berzelius to determine 

 the composition of boracic acid, given in the Annals of Philo- 

 sophy, XV. 278, are merely a republication of the experiments 

 made by him some years ago, and first published in an early 

 volume of the Annals of Philosophy. I am still of opinion that 

 the constitution of this acid which I have given in the fifth 

 edition of my System of Chemistry, is the nearest the truth, 

 according to the present state of our knowledge. I have lately 

 had an opportunity of repeating and verifying some of the expe- 

 riments on which this constitution was founded. 



2. Phosphorous Acid. — Berzelius, in a set of experiments 

 published some years ago in the Ann. de Chim. et de Phys. has 

 endeavoured to prove that the oxygen in phosphorous and phos- 

 phoric acids are to each other as the numbers 3 and 5. I have 

 stated shortly, but I trust with sufficient clearness, the reasons 

 that lead me to conclude that the oxygen in phosphoric acid is 

 exactly twice as much as that in phosphorous acid, and that the 

 composition of the two acids is as follows : 



Phosphorous Acid. 



1 atom phosphorus = 1*5 



1 atom oxygen = 1*0 



¥5 

 Phosphoric Acid. 



1 atom phosphorus = 1*5 



2 atoms oxygen = 2*0 



¥5 



If the reader will turn to Annals of Philosophy , xv. 227, he 

 will find the evidences on which the truth of this opinion depends. 



3. Sulphuric Acid. — The latest experiments of Berzelius on 

 the constituents of this acid {Annals of Philosophy, xv. 96) make 

 it a compound of 



Sulphur 100-00 



Oxygen ] 48-44 



This is a considerable approximation to the true composition, 

 and indeed the nearest hitherto obtained by experiment. It is a 

 ^ood deal nearer the truth than any of his preceding determina- 

 tions ; but it is easy to show, and I have done so in the last 



