138 Review of Dr. Thomson 



It is diverting to see the pertinacious effrontery with which he 

 still refers to his experiments on oxalic acid, after the full expo- 

 sure of their absurdity, in our review of his system, (6th edition,) 

 and in our remarks on his answer to that review *. 



He now sets to work, in his usual way, on the crystalline hy- 

 drate, to ascertain, whether or not, oxalic acid contains hydrogen. 

 This point has, however, been determined so fully by the most 

 delicate and decisive experiments, as utterly to supersede Dr. 

 Thomson's tardy intervention. 



Dr. Thomson's experiments to ascertain the atomic weight of 

 tartaric acid betray a rudeness in practical chemistry, unaccount- 

 able in so old a hand. He describes tartrate of potash, as con- 

 taining two atoms of water, separable by heat. The anhydrous 

 salt has, according to him, an atomic weight of 14.25, to which 

 8.25 sea 2 atoms of water being added, the sum 16.5 will be the 

 number of the crystallized salt. 14.25 of the anhydrous salt, 

 corresponding to 16.5 of the crystals, were found by him exactly 

 equivalent to 20.75 of nitrate of lead. " The mother water (of 

 the mixed solutions of these two salts) was tested with nitrate of 

 lead, and tartrate of potash, without being in the least affected 

 by either. Hence it contained no sensible quantity either of tar- 

 taric acid or of lead. The whole of these two bodies was contained 

 in the precipitate which had fallen." 



His number for tartrate of potash is unquestionably wrong ; 

 and, indeed, though it were right, his conclusion would be erro- 

 neous. For the mother water (as he elegantly terms the limpid 

 supernatant liquid) contains, under his proportions, both tartaric 

 acid and oxide of lead. Let it be tested with sulphate of soda, 

 and it will become cioudy ; with sulphuretted hydrogen, and it 

 will become very black ; or with nitrate of lead, and tartrate of 

 lead will fall. Thus the principle of Richter, of whose applica- 

 tion our Doctor is so vain, becomes, under his management, quite 

 deceptious. 



His determination of the atomic weight of acetic acid is liable 

 to the same objections. He mixes solutions of 8.875 gr. of oxa- 

 late of ammonia (its true atomic weight appropriated as usual to 

 himself, from a prior memoir in the Phil. Trans, for 1822) and of 

 23.625 grains of acetate of lead ; and tests the supernatant li- 

 quid " by sulphate of soda and muriate of lime." Now we have 

 the pleasure of informing the Regius Professor of Chemistry, 

 that as a test of lead, sulphate of soda is good for very little on 

 the present occasion ; and indeed no accurate chemist would trust 

 to it. Acetate of lead and sulphate of soda can co-exist to a very 

 considerable extent in a clear solution ; as the youngest tyro may 

 prove, by adding to one portion of the supernatant liquor, muriate 



* Quarterly Journal, xi. 155, and iii. 349. 



