TRANSACTIONS OF THE SECTIONS. 33 



yields up its chemical characters on uniting with other bodies. The iron in pro- 

 toxide of iron has still an affinity for more oxygen, and has not lost that affinity by 

 its first union with that element. The intensity of affinity, by which the simple ele- 

 ments are joined in the complex molecule, must be the measure of the stability of 

 the compound. Mr. Mercer argued, that when the elements of a body are in mere 

 static equilibrium, by virtue of a feeble attraction, and when it is acted upon by 

 another body possessing an affinity for one of its constituents, which constituent, on 

 the other hand, from peculiar circumstances, is not prone to combine with it, that 

 in such a case so-called catalysis must ensue. Thus, on mixing oxalic acid and 

 nitric acid with a little water, and raising the temperature to 130°, no action ensues. 

 But if a small portion of any protosalt of manganese be now added, the decom- 

 position immediately commences, and all the nitric is converted into nitrous acid, 

 whilst the oxalic acid passes into carbonic acid. He thus accounts for this singular 

 action : — The carbonic oxide of the oxalic acid possesses a disposition to unite with 

 oxygen. To gratify this disposition, it endeavours to withdraw it from nitric acid, 

 but is not sufficiently powerful to do so ; still it places the atoms of the nitric acid 

 in a state of tension. Another body (protoxide of manganese) now being introduced, 

 which also possesses an affinity for oxygen, exerts this affinity, and the combined 

 forces thus acting upon the nitric acid occasion its decomposition. The moment the 

 oxygen is withdrawn from its state of combination, it has two affinities to choose 

 between, and the attraction of the oxalic acid being greater, it passes over to it, con- 

 verting it into carbonic acid. The protoxide of manganese still remaining will act 

 on fresh portions ad infinitum. Most of the vegetable acids may be decomposed in a 

 similar manner. Following up this view, Mr. Mercer had discovered a number of 

 examples of what formerly would have been called catalysis. He showed, that 

 when alumina (precipitated from a hot solution) is placed in contact with dilute nitric 

 acid, no apparent action ensues. But as Dr. Playfair had described a peroxide of 

 aluminium, it ought to have a disposition to unite with oxygen. To discover then 

 whether the atoms of nitric acid were actually in a state of tension, he introduced a 

 slip of calico rendered blue by indigo. When this came in contact with the preci- 

 pitated alumina, the indigo was immediately discharged, although it remained un- 

 affected in the supernatant liquor. Chlorous acid was a body well fitted for his 

 purpose, as its elements were held together by a feeble affinity, and as its oxygen was 

 very readily yielded. He showed that the peroxide of copper, discovered by Dr. Play- 

 fair, occasioned a great evolution of oxygen from a solution of chloride of soda. 

 This was owing to its endeavour to become cupric acid, which under certain cir- 

 cumstances it did form. He had noticed many years since that a dark purple solu- 

 tion is obtained on mixing chloride of lime, a salt of copper, and lime with water, 

 and leaving the mixture at repose. No evolution of oxygen is occasioned by this 

 purple solution, but by the peroxide of copper before passing into it. Peroxides of 

 manganese and cobalt exert a similar action. The reason was, that these metals 

 possessed only a feeble affinity to pass into the metallic acids. Still the affinity was 

 sufficient to occasion the withdrawal of oxygen from chlorous acid. The moment it 

 was withdrawn elasticity came into play, and it escaped as a gas. A similar action 

 is exerted by the peroxides of iron and lead. From these and several other instances 

 which were described, Mr. Mercer concluded that almost all instances of catalytic 

 action may be reduced to feeble chemical affinity. He concluded by some specula- 

 tions on the atomic constitution of complex molecules. 



On Hcematoxylin, the Colouring Principle of Logwood. By Professor 

 O. L. Erdmann of Leipsic. 



The hammtoxylin used by the author in his experiments, was prepared by the 

 process of Chevreul. In a state of purity hsematoxylin is not red ; it is in itself no 

 colouring matter, being merely a substance capable of producing colouring matters 

 in a manner similar to lecanorin, orcein, or phloridzin. The colours which it pro- 

 duces are formed by the simultaneous action of bases (particularly strong alkalies), 

 and the oxygen of the atmosphere. By the action of these it undergoes a process of 

 eremacausis, which, after forming colouring matters, ends in the production of a 

 brown substance resembling mould. 



1842. D 



