the Colouring Matters of Madder. 189 



Rubian. Sugar. Alizarine. Rubiretine. 



C32 H i8 O i8* = c i2 H 12 O 12 H-C 10 H 3 O 3 + C 10 H 4 O 3 -2aq. 



In this equation verantine may be substituted for the aliza- 

 rine, since, according to M. Laurent, the formula of the former, 

 C 20 H 7 O 7 , differs merely by HO from the double of that of aliza- 

 rine, C 10 H 3 O 3 . In the same manner, the rubiretine, by adopting 

 M. Laurent's formulae, may be replaced in this equation by ru- 

 bianine. 



M. Laurent has prefaced his observations by the enunciation 

 of several propositions or laws, as, for instance, " In all organic 

 substances the number of atoms of each simple substance is even," 

 &c. It is in accordance with these propositions that he has 

 made the alterations in the formulae proposed by me. 



It will be conceded by most chemists, that the chemical for- 

 mula of a body is of no interest or importance except as exhibit- 

 ing the relation in which the body stands to others. Indeed we 

 may go further, and say that in many cases, especially those 

 of bodies of high atomic weight, it is immaterial for most pur- 

 poses whether the formula be absolutely correct, provided it be 

 relatively so. What is required of a chemical formula is, that it 

 should be in accordance with the analysis, that it should show 

 the connexion subsisting between the composition of the body 

 and that of others, and that it should be in harmony with what 

 we know of its mode of formation and its products of decompo- 

 sition. Whether it is in accordance with any empirical law re- 

 garding the number and arrangement of atoms represented by 

 it, or not, is quite immaterial ; for the object of chemical inves- 

 tigation, of which formulae shortly express the results, is not the 

 discovery of mathematical laws, but of chemical facts. Now the 

 formulas proposed by M. Laurent for the substances described 

 by me do not fulfill any of the conditions required. They do not 

 agree as well as mine with the results of analysis, and they quite 

 fail to explain the mutual interdependence which I have shown 

 to exist between these various bodies, as well as the nature of 

 the processes whereby one original substance splits up into so 

 many derivatives. I readily concede, that, looking at each sub- 

 stance alone, it would be possible to discover a number of for- 

 mulas agreeing better than mine with the results of analysis ; 

 but it is impossible, as I have shown, to consider the composition 

 of any one of them out of connexion with that of the others ; it 

 is necessary to look at them from a point of view common to all, 

 to construct some system which shall include them all, even by 



* This formula has been given three times, or else it might be concluded 

 that there was a misprint in the numbers, as the equation is impossible as 

 it stands. 



