342 Analysis of Scientific Books. 



" Operating in this way," says Sir H. Davy, " I find that iodine 

 absorbs less than one tliird of its weight of chlorini-." " In 

 another experiment in which the sublimate was not dissolved by 

 water, and in which the absorption was judged of, by the ad- 

 mission of fresh quantities of the gas, twenty grains of iodine, 

 caused the disappearance of 9.6 cubical inches of chlorine.*" 

 The mean of these two results gives very nearly one atom of 

 chlorine to one atom of iodine, for the composition of chlorio- 

 dicacid. Dr. Thomson omits, purposely it would appear, the' 

 statement above quoted, and brings forward another experiment, 

 in which, from the admission of water, the same precision could 

 not be obtained by that philosopher. He thus seeks to shew, 

 that Sir H. Davy is in the wrong, relative to the atomic pro- 

 portions, and that he himself is right, in pitching two atoms of 

 chlorine against one of iodine. 



The diXUcXe. phosphoric acid in his "Answer," contains an unfor- 

 tunate anachronism which it will ])uzzle his veracity to reconcile. 

 " Soon after this, I went to Glasgow (September or October, 

 1817), and I was not in possession of a laboratory for nearly 

 two years. One of the first thirigs which I did as soon as it was 

 in my power, was to repeat Dalton's experiment (on phosphu-" 

 retted hydrogen). I found it inaccurate. The whole structure 

 immediately tumbled to the ground; and I was led back to the- 

 original opinion which I had stated in my paper on phosphu- 

 retted hydrogen gas. And those gentlemen who attended my 

 lectures the ensuing course, will remember that I then gave the 

 composition of phosphorous and phosphoric acids, precisely as 

 in my sixth edition. Davy's paper appeared soon after, and 

 confirmed me in the accuracy of my experiments.!" Dates are 

 fatal to our Doctor's statement. He gives us here to under- 

 stand, that nearly two years after his arrival in Glasgow, that 

 is in the autumn of 1819, he was put in possession of a labora- 

 tory ; and one of the first things he did in it, was to repeat Dal- 

 ton's experiment. He adds " Davy's paper appeared soon 

 qfter." We marvel at his venturing to publish so palpable a 

 falsehood. For in his Amials for May, 1818, we have an ac?- 

 count of Sir H. Davy's paper, on phosphorous and phosphoric 

 acids, which had been read before the Royal Society on the: 

 preceding ninth of April. 



The following is Thomson's notice, fifteen months before he' 

 was in possession of a laboratory; " In the hypophosphoric 

 acid the proportions will be 45 phosphorus, to 15 oxygen. 



:.■. (3. : 1.0) .. 



In phosphorouf acid 45 to 30 (1.5 : 1.0) 



And in phosphoric acid 45 to 60 (1.5 : 2.) 



" On some future occasion, we hope to give a more complete 

 • PM. Trans, for 1814, part ai. f Answer p. 361. 



