of simple alimentary Substances, fyc. 109 



cumstances of the atmosphere, was found (abstracting foreign 

 matters) to consist of 



Carbon 36*3 



Water 63*7 



One hundred parts of the same gum, exposed to a tempera- 

 ture between 200° and 212°, for upwards of twenty hours, lost 

 12*4 parts. Hence its composition thus dried would be nearly 



Carbon 41*4 



Water 58.6 



results confirmed almost exactly by actual analysis. 



The same gum, further exposed to a temperature between 

 300° and 350° for six hours longer, assumed a deep brown 

 colour, and seemed to have suffered decomposition, though it 

 lost in weight only 2*6 per cent. more. Hence, gum probably 

 parts with the whole of the water not essential to its composi- 

 tion at the temperature of 212°, provided it be exposed for a 

 sufficient time to this degree of heat. 



Substances belonging to this series appear in general to be 

 of a weak or low kind, though they are probably very numer- 

 ous. They may be readily distinguished by being converted 

 into saclactic acid by the action of nitric acid. 



The vegetable Acids. 

 Oxalic Acid. — Many years ago I ascertained that this acid 

 in the crystallized state consists of 



Carbon 19*04 



Water 42-85 



Oxygen 38*11 



a composition assigned to it long since by other chemists, and 

 now I believe generally admitted, except by Dr. Thomson, 

 who informs us that he has met with a specimen containing as 

 much as half its weight of water*. I have examined a great 

 many specimens with the view of verifying this result, but 

 hitherto have not been successful. 



Citric Acid. — This and all the following acids, except the 

 malic, were analysed at the same period as the oxalic acid 

 above mentioned, and the results have been recently verified. 

 I find the crystals of citric acid to consist of 



Carbon 34*28 



Water 42*85 



Oxygen .... 22*87 

 This composition has been approached very nearly by se- 

 veral chemists ; but no one, so far as I know, has given it ex- 

 actly. 



* Attempt to establish the first principles of chemistry by experiment, 

 ii. 103. 



Tartaric 



