J4 On the Definite Proportions in which the [Feb 



volumes, we find that they agree perfectly with the idea that citric 

 acid is composed of equal volumes of its elements ; that is to say, 

 it ought to coutain per cent. : 



Hydrogen 3*634 



Carbon 41-270 



Oxygen 55-09G 



100-000 



If this be so, citric acid has the simplest composition of any of 

 the ternary oxides. Its capacity of saturation indicates that it ought 

 to contain four volumes of oxygen, four volumes of carbon, and 

 four of liydrogen. Must we consider it as a compound of I'i atoms 

 or of three? Experiments on the combination of citric acid with 

 water seem to prove tliat it contains only three atoms, an atom of 

 each constituent. 



When we compare the result of my former experiments on the 

 quantity of water contained in citric acid, we find that they do not 

 coincide with the result of the analysis of citrate of lead. 10 parts 

 of citric acid in crvstals dissolved in water, neutralized by ammonia, 

 and mixed wi;h nuiate of lead, as long as any precipitate fell, pro- 

 duced 2i'']bii of dry citrate of lead. In this citrate there is 8*3 of 

 citric acid; that is to say, that 100 parts of acid contain 17 of 

 water: or that 100. parts of acid combine with 20'5 of water, 

 which contain 18*1 oxygen. But IS'l x 3 = 54-3; that is to 

 say, that in crystallized citric acid the acid contains three times as 

 much oxygen :is the water. 



I look five })arts of citric acid reduced to a coarse powder, and 

 exposed them in a glass capsule exactly weighed to a temperature 

 between 1 18° and VI'JP. In 24 hours it lost 0-43 of its weight, 

 and had assumed the form of a white light powder. In another 

 experiment the loss was 0-424. No further loss was sustained by 

 longer exposure to heat. This experiment shows that citric acid by 

 efflorescing loses fiom 8-.)8 to 8-6 per cent, of its weight of water, 

 which is obviously the half of the water of crystallization contained 

 in the acid. Citric acid does not part with the rest of its water; 

 for if we heat it to a certain temperature, it loses indeed weight, 

 but at the same time it becomes brown, is decomposed, and leaves 

 a brownish deliquescent mass, no longer possessing the properties 

 of citric acid. In order to expel the water we must substitute 

 another oxide in its place. From these experiments it follows, that 

 in effloresced citric acid, or citrate of water, as it may be called, 

 the acid contains six times as much oxygen as the water, and that in 

 crystallized citrate of water the acid contains three times as much 

 as the water. 



This property of citric acid to allow itself to be saturated by 

 water in another proportion than by the stronger oxides is pecu- 

 liar; but it is easily explained by the simplicity of the compositloB 



