CHEMICAL BASIS OF THE ANIMAL BODY. 117 



Acetic acid. CH 3 . COOH. 



Is distinguished by its characteristic odour ; its boiling point is 

 118 C. ; the anhydrous acid solidities at about 17. It is soluble in 

 all proportions in alcohol and in water. 



It may be formed in the stomach as the result of fermentative changes 

 in the food, and is frequently present in diabetic urine as also in traces 

 in normal urine. In other organs and fluids it exists only in minute 

 traces. 



With ferric chloride it yields a blood-red solution, decolourised by hydrochloric 

 acid. (It differs in this last reaction from sulphocyanide of iron.) Heated with 

 alcohol and sulphuric acid, the characteristic odour of acetic ether (ethyl- acetate) 

 is obtained. 



Acetone. CH 3 . CO . CH 3 . 



This substance is the typical member of the general class known as 

 ketones and may be prepared by the dry distillation of calcium or barium 

 acetate. 



Ketones are characterised by containing the group CO (carbonyl) in the same 

 way that the aldehydes are characterised by the group COH, and the acids by the 

 group COOH. The ketones are closely related to the aldehydes and may be 

 regarded as derived from them by displacing the H of the COH group by some 

 monad (alcohol) radicle. They are most usually prepared by the dry distillation of 

 the calcium salts of the appropriate acids. Ketones, like the aldehydes, unite 

 readily and directly with phenyl-hydrazin, yielding a class of compounds, known 

 as hydrazones. (Cf. p. 102.) 



Acetone is a volatile liquid, soluble in water, boiling at 56, and 

 possessed of an agreeable ethereal odour. It may be obtained in 

 considerable quantity by distillation from the urine and blood of 

 diabetic patients and accounts for the peculiar ethereal odour which 

 these frequently evolve 1 . This symptom is of serious prognostic im- 

 portance, and it has been supposed by many authors that the fatal 

 diabetic coma which rapidly supervenes is caused by the presence 

 of acetone 2 . The urine of diabetic patients frequently exhibits a 

 reddish-violet colouration with ferric chloride supposedly due to the 

 presence of aceto-acetic acid (CH 3 . CO . CH 2 . COOH) which readily 

 yields acetone by its decomposition. 



Acetone is also not infrequently found in the urine and breath (?) of 

 children in apparently normal health 3 . 



Acetone gives a characteristic reaction with iodine in presence of an 



1 Von Jaksch, Ueber Acetonurie u. Diaceturie, Berlin, 1885. Gives history and 

 literature of the subject. Cf. Zt. f. physiol. Chem. Bd. vi. (1882) S. 541. 



2 Cf. Gamgee's Physiol. Chem. Vol. i. 1880, 'p. 168. 



3 Baginsky, Arch. /. Physiol. Jahrg. 1887, S. 349. 



