250 Dr, Thomson's Amwer to the Review of the [April; 



experiments were deficient in correctness, the reason was, that 

 minute accuracy in chemical analyses did not at that time appear 

 to me an object of primary importance. The knowledge of the 

 atomic theory has altered my views in this respect. All my 

 recent experiments have been made with the most scrupulous, 

 attention, and the results which 1 have given in seven different 

 papers on the specific gravity of gases, and the atomic weights of 

 bodies, are as near the truth, as it was possible for me to go 

 with the apparatus which I employed. 



Let not this statement be warped (as the Reviewer has 

 done) into an insinuation that I lay claim to any superiority 

 in experimental dexterity. So far from this, I consider the 

 accuracy of my results to be in reality owing to my want 

 of dexterity ; for it obliged me to look out for a method in 

 which no dexterity was required. There is little difficulty in 

 procuring the substances to be experimented on, pure. There 

 is little difficulty in weighing the quantity wanted, true to 

 the hundredth part of a grain ; in dissolving it in distilled 

 water ; and in mixing two such solutions together. Such is the 

 whole process. Any person, however little dexterity he may 

 possess, will succeed in such experiments, if he be at the requi- 

 site pains. For example, I weigh 11 grains of sulphate of 

 potash, and 13-25 grains of chloride of barium ; dissolve each 

 respectively in distilled water, and mix the solutions. After the 

 sulphate of barytes has subsided, I test the clear supernatant 

 iiquid by mixing a little of it first with muriate of barytes, and 

 next with sulphate of soda. Not the least opalescence is pro- 

 duced by either. Hence I conclude that the liquid contains no 

 sensible quantity either of sulphuric acid or of barytes. This 

 experiment, simple as it is, determines the composition of sul- 

 phate of barytes to be : 



Sulphuric acid 5*0 



Barytes 9*75 



14-75 



And demonstrates that 5 and 9*75 respectively represent the 

 atomic weight of sulphuric acid and barytes. 



The Reviewer asks with a sneer (Review, p. 124), whether the 

 preceding experiments of Berzelius, Wollaston, &c. are to be 

 considered as good for nothing, and whether they are to be 

 superseded by mine. T beg leave to ask in my turn whether 

 the experiments of Bergman, Wenzel, Kirwan, and Richter, 

 were good for nothing, and whether they areXo be supersedea 

 by those of Berzelius, Wollaston, &c. 'i The object of every 

 experimenter is to discover the truth ; but, from the imperfect 

 nature of his apparatus, he only makes an approximation. His 

 result serves his successors as a point from which they are 

 enabled to set out ; and if they be at the requisite pains, the 



