of Phosphoric Acid. 279 



and 3 oxygen. Thomson on the contrary makes, in the " First 

 Principles," phosphorous acid an atoni of each ; and phospho- 

 ric, 1 phosphorus and 2 oxygen; to which he has since added 

 a third acid (Phil. Mag. and Annals, vol. v.), of 1 phosphorus 

 and 3 oxygen. An extract from Dr. Henry's " Chemistry," 

 in your Number for the present month (March) is favourable 

 to the views of the Swedish Professor, but with some expres- 

 sions of indecision (regarding the uncertain composition of the 

 phosphuretted hydrogen gases). The acid determined by 



Davy to consist of ...' phosphorus 100, oxygen 134-5 



and by Berzelius of 100 133 



is regarded by Thomson as 1 phosphorus and 2 oxygen ; which 

 opinion has some analogical corroboration from the constitu- 

 tion of the acid obtained from sulphur by Davy's process, i. e. 

 combustion in oxygen. But the process of Berzelius, solu- 

 tion and cohobation (if the term may be so applied) with nitric 

 acid, giving with sulphur an acid of 3 oxygen, the analogy 

 fails, unless in the latter process phosphuretted azotic gas was 

 formed, and ^rd of the phosphorus thus wasted ; — a case so 

 improbable, that nothing less than the decisive experiments 

 in the " First Principles," on acid of atomic weight 3*5, would 

 have allowed the supposition to be entertained. 



Combustion in chlorine and subsequent solution in water 

 would be subject to the same uncertainty as combustion in 

 oxygen, unless obviated by a current of chlorine through the 

 solution. The following was however preferred : 



Phosphorus melted in warm water was sucked up into 

 a long glass tube, and there kept fluid until foreign matters, 

 sinking or floating according to their specific gravity, had left 

 the greater portion of it transparent and almost colourless. 

 How to purify that substance more effectually, I do not know. 

 12-05 grains of the transparent part was put into a Woulfe's 

 apparatus under water, and a current of chlorine gas, issuing 

 close by the phosphorus, slowly passed. The phosphorus 

 being little diminished alter a week's continuance in this, the 

 apparatus was opened, and a small test tube introduced, into 

 which were inserted the end of the tube from the generator, 

 and the phosphorus, so that the bubble of chlorine should rise 

 along it. The action thus expedited, the bubbles rose cloudy, 

 settling as a dense vapour on the surface of the water, and in 

 two days the phosphorus was completely dissolved. On open- 

 ing the apparatus the solution of phosphorus became turbid, 

 and the sides of the bottle opacjue and greasy, as though it 

 were charged with powdered spermaceti. Although tempted 

 by this new appearance, I preferred continuing the experi- 

 ment as begun, and after leaving the tubuiurc open three days, 



t!ic 



