on the Atomic Theory. 137 



atomic weights of the above metallic bodies, nothing can be more 

 unsatisfactory. We are persuaded that his numerical results 

 would be less equivocally obtained, by a collation of the experi- 

 ments of other chemists with the modern atomic theory, than by 

 any inference from his own researches. 



" 1 found many years ago," says he, " that when 100 parts of 

 iron are oxidized by passing the steam of water over them at a 

 red heat, they combine with 29.7528 parts of oxygen *." But 

 from the experiments of M. Gay Lussac, it is known, that 100 

 parts of iron oxidized in this way, unite with 37.8 parts of 

 oxygen. So much for the Doctor's experimental precision. 



Now for his theoretical profundity. " Hence it would appear 

 that this supposed oxide (of Gay Lussac), is a compound of 1 

 atom iron + l\ atom oxygen gas t." 



We cannot devote much time to his second volume. Persons 

 who can find amusement in haphazard experiments and gratuitous 

 inferences may look into his section on uranium, particularly 

 the 4th and 5th pages. M. Arfwedson made some good researches 

 on the combinations of this metal with oxygen, which Dr. Thom- 

 son as usual turns to his own account, by slight modifications. 

 " To determine the atom of chromium I dissolved a quantity of 

 chromate of potash in water, and added tartaric acid to the so- 

 lution. An effervescence took place, and the solution assumed a 

 fine green colour, because the chromic acid was converted into 

 protoxide of chromium. Ammonia being poured into the green 

 coloured liquid, the protoxide of chromium was precipitated. It 

 was collected on a nitre, well washed, and dried in the open air J." 



Now we affirm that this experiment, from which he deduces the 

 atomic weight of chromium, was never made, for the result is im- 

 possible. Ammonia does not precipitate oxide of chromium from 

 the above green solution in tartaric acid. 



When solutions of chromate of potash and tartaric acid are 

 mixed, there is an immediate formation of bitartrate of potash, 

 which speedily falls down ; and if the tartaric acid be in consider- 

 able excess, the chromic acid will be decomposed with efferves- 

 cence. But the oxide in the resulting green liquid is not preci- 

 pitable by ammonia. Yet Dr. Thomson builds upon a pseudo-ex- 

 periment, one of his usual atomic structures. Ex uno disce omnes. 



Our readers must, by this time, be nearly as tired, as we have 

 long been ourselves, of this illusory and fantastic attempt. 



He assigns 9 for the atomic weight of crystallized oxalic acid. 

 The number 7.875 first given in the Philos. Trans, for 1822, is 

 undoubtedly more to be depended on, particularly since it has 

 been confirmed by *' a chemical friend, of whose accuracy and in- 

 formation I (Dr. Thomson) entertain a very high opinion §." 



* Attempt, i. 355, t Jbid. % Ibid. ii. 51. $ Ibid. ii. 103. 



