1815.] Elements of Organic Nature a^e combined. 181 



Gay-Lussac and Thenard found mucous acid composed of 3'62 

 per cent, hydrogen, 33 69 carbon, and C2*69 oxygen. This (the 

 hydrogen excepted) does not differ much from my result. 



When we compare the analyses of the tartaric and mucous acids, 

 we find between them so little difference, that we should guess their 

 composition to be very analogous. Yet we see by the analysis of 

 mucate of lead, and by the capacity of saturation of mucous acid, 

 that the arrangement of their atoms is very different. 



8. Benzoic Acid. — The benzoate of lead is a light crystalline 

 powder, slightly soluble in water. When heated in a temperature 

 somewhat higher than that of boiling water, it melts, and gives out 

 3"85 per cent, of water. If the heat is too long continued, or 

 raised a little higher, a portion of the acid begins also to evaporate. 

 W^e must, therefore, employ a retort, to determine the water of 

 combination of this salt ; for if a little acid should sublime, it will 

 be deposited on the upper part of the retort. 



Three parts of benzoate of lead, cautiously melted, and treated 

 with sulphuric acid diluted with alcohol, produced 1'933 of sulphate 

 of lead, equivalent to 1-4505 of oxide of lead. Hence benzoate 

 of lead is composed of 



Benzoic acid ..s 51'(J5 .... 4i)-66 .... 100 



Oxide of lead 48-35 4G-4D .... 93-61 



Water 3-S5 



100-00 100-00 



Now these 46-49 of oxide of lead contain 3-32 of oxygen, and 

 the 3-85 of water contain 3-39 oxygen ; so that the water and oxide 

 of lead contain equal quantities of oxygen. 



Fused benzoate analyzed by combustion gave 49*125 per cent, of 

 oxide of lead, which makes 94-05 for 100 of acid. Hence this 

 acid neutralizes a quantity of base containing from 6*69 to G-72 of 

 oxygen. 



Neutral benzoate treated with concentrated ammonia gives a 

 subbenzoate, which being analyzed by combustion gives 74 per 

 cent, of oxide of lead. Though long exposed to a high tempera- 

 ture, it gives no trace of water, not even when its acid begins to be 

 disengaged. Hence it is composed of 



Benzoic acid 26 100 



Oxide of lead 74 284*6 



100 



But 94 X 3 = 282. Therefore benzoic acid ought to contain 

 three volumes of oxygen. 



The analysis of benzoic acid cost mc much more trouble than 



any of tlie others owing to a circumstance which I was long in 



discovering. Its weak alVmiiy and great volatility occasions the 



evaporation of a portion of it during the combustion. The portion 



(i 



