354- Mr. Connell on the Nature of Lampic Acid. 



acids vary somewhat according to the mode of preparation, 

 which seems to follow from the late experiments, negatives 

 this idea ; and indeed it is given up by Liebig, who now only 

 says, in his Organic Chemistry, that aldehydic acid is one of 

 the acids in lampic acid. But if we take the above-mentioned 

 normal mode of preparing it, — the method principally used by 

 Davy, Faraday and Daniel], then formic acid constitutes by 

 much the larger proportion of the acid liquid so prepared ; 

 and as formic acid is well known to reduce the oxides of me- 

 tals having feeble affinities for oxygen with effervescence, it is 

 plain that this characteristic property of lampic acid may be 

 with justice mainly ascribed to its formic constituent. 



But the more important point is, whether lampic acid con- 

 tains any aldehydic acid at all. On this, I think I shall be 

 able to show that the experiments depended on are quite insuf- 

 ficient to establish this fact; and that my own experiments, as 

 well as those of Mr. Daniell, are opposed to such a view. It 

 is admitted on all hands that there are other matters besides 

 acids present in the liquid to which the name of lampic acid 

 is usually given. Of these aldehyde is certainly one. Now 

 every one of the late experiments is quite explicable on the 

 idea, which indeed is advocated by Martens, that this aldehyde 

 is mixed or otherwise associated with the acetic acid which 

 remains after the formic acid has been removed by means of 

 oxide of lead or otherwise. Thus the acid supposed to be the 

 aldehydic portion of lampic acid is described as reducing ni- 

 trate of silver without effervescence ; as yielding a brown resin 

 when heated with alkali, and as affording a copper salt, which 

 when heated in solution gives a precipitate of suboxide of cop- 

 per, whilst acetate of copper is formed and remains dissolved. 

 Now as it is a character of aldehyde to reduce certain metals 

 without effervescence, and to yield a resin when heated with 

 an alkaline solution, all the above experiments are quite compati- 

 ble with the idea that the acid is merely the acetic with asso- 

 ciated aldehyde. The same view will readily explain Liebig's 

 argument, founded on the darkening of the lampic salts on 

 evaporation, and of the acid itself by sulphuric acid. All 

 these are characters which the presence of aldehyde would 

 produce. 



But my own experiments, as well as those of Mr. Daniell, 

 on the atomic weight of lampic acid, as prepared by the ordi- 

 nary process, afford still more direct evidence on this point. 

 By an analysis of the lampate of barytes I ascertained the 

 atomic weight of the acid to be 50*35 or 6294, oxygen = 100 ; 

 and Mr. Daniell's result was quite the same. Now the atomic 

 weight of formic acid is 37; that of acetic acid 51; that of the 



