54 ATOMIC WEIGHTS. 



analysis of Gay-Lussac, Dr. Prout, and others, 

 that perfectly dried wood is composed of about 

 50 parts by weight of carbon, to 50 of oxygen 

 and hydrogen in the proportions that form water. 

 M. M. Petersen and Schodler have also found 

 recently, by an important series of experiments 

 on 24 different species of wood, that they are 

 composed of carbon, oxygen, and hydrogen, in 

 very nearly the same proportions by weight : and 

 it is certain that definite ratios of oxygen com- 

 bine with their carbon and hydrogen during com- 

 bustion. They found that lOOlbs. of lime- wood 

 absorb and combine with 140*523lbs. of oxygen 

 and that 100 Ibs. of beech, which required less 

 oxygen than any of the 24 species, combined with 

 130-834 Ibs. of oxygen. (Journal of Prac. Sci- 

 ence, Nov., 1836.) It was formerly maintained 

 by Gay-Lussac and Thenard, that vegetable 

 substances are acid when they contain a larger 

 proportion of oxygen than is required to form 

 water resinous, oily, or alcoholic, when the quan- 

 tity of hydrogen predominates and saccharine, 

 mucilaginous, &c., when there is no excess of 

 either oxygen or hydrogen. Though exceptions 

 have been found to their results, they are true in 

 so many cases, that it is well to bear them in 

 mind. 



The recent progress of chemical science has 

 led to the discovery of some apparent excep- 

 thus to the law of multiples. The following ex- 

 amples have been indicated by Dr. Turner. The 



