1815,] Elements of Organic Nature are combined. 271 



But we see that gum arable ought to contain 12 times as much 

 water as the base by which it is saturated : for 4*44 x 12 = 53-J8. 

 This small difference ought to be ascribed to a small error in the 

 analysis, or in the preparation of gummate of lead ; wliich error is 

 in the present case increased 12 fold in the calculation. But if 

 gum arable contain 12 atoms of oxygen It must contain 13 of car- 

 bon and 24 of hydrogen, which make in 100 parts 



Hydrogen 6'7n2 



Carbon 41*752 



Oxygen 51*456 



100*000 



This agrees very well with the result of direct experiments. Gum 

 arable then Is 12 O + 13 C + 24 H. 



The analysis of Gay-Lussac and Thenard gave 6-93 hydrogen, 

 42*23 carbon, and 50*84 oxygen. 



1 ought to observe, tliat in my experiments, gum, whether pure 

 or combined with oxide of lead, "produced traces of nitric acid ; so 

 that what in the analysis I considered as pure hydrogen, contains in 

 fact a trace of the radicle of nitric acid : which, as is known, has 

 the same capacity for oxygen that hydrogen has. 



I am, however, far from pretending that gum arable contains 

 nitricum among its elements. It Is more probable, that the forma- 

 tion of the nitric acid is owing to the presence of a small quantity 

 oi vegetable albumen in the gum. Probably the excess of -i- of a 

 per cent, of carbon obtained in the analysis, is owing to the same 

 cause. 



Gum arable, wlien incinerated, leaves a small quantity of aslies, 

 the weight of which is very variable ; and, of coui-se, it cannot he 

 considered as an essential constituent of the gum. So much the 

 less, as i)oth Vauquelln and Cruikshaiiks found that gum contained 

 vegetable salts with a l)ase of lime. To see whetiier gum contained 

 any secondary clement, 1 endeavoured to separate it from gummate 

 of lead. 1 found that this could not be accomplished either Ijv 

 means of sulphuric a(;id, or sulphureted hydrogen ; for the disen- 

 gaged gum causes the insoluble |)recipltates to pass through the 

 liiter, and it prevents tiieiii from being ever deposited. I therefore 

 dissolved gummate of lead in acetic acid, and into the solution 1 

 poured alcohol, which precipitated the gum. 1 washed the gum 

 very well in alcohol. 'Ihis gum, being dried and burnt in a glass 

 capsule, left oxide of lead, retained probahly in the state of a 

 supcr-gummatc of lead, 'i'he ashes were easily soluble in acetic 

 acid. The liquid being evaporated to dryness, and burnt, left sul- 

 phate of lime, with traces of sulphate of potash, weighing together 

 4 of a per cent, of the gum. But sulphuric acid constituting more 

 tluui one half of these a>lies, it appears that the small quantity of 

 the radicles of the bases cannot he considered as of any value in the 

 con)positiuii of gum arable. 



