MONOBASIC FATTY ACIDS. 505 



'Trichlor-acetic acid, Acidum trichloraceticum, CC1 3 .CO 2 H 

 162.12. As shown in the previous paragraph, this acid may be ob- 

 tained by the direct action of chlorine on acetic acid, but it is usually 

 made by the oxidation with nitric acid of chloral (tricolor-aldehyde), 

 which requires but one atom of oxygen for its conversion into tri- 

 chlor-acetic acid. 



Trichlor-acetic acid is a white, deliquescent, crystalline substance. 

 It has a slight, characteristic odor, is readily soluble in water, alcohol, 

 and ether. The aqueous solution, on boiling, is decomposed into 

 chloroform and carbon dioxide. It is used as a local caustic and as 

 a reagent for albumin. 



Acetyl chloride, CH 3 .COC1, is obtained by distilling a mixture of 9 parts 

 of glacial acetic acid and 6 parts of phosphorus trichloride on a water-bath at 

 a slightly elevated temperature. It is a colorless liquid, having a suffocating 

 odor, boiling-point of 55 C., and specific gravity 1.13 at C. It fumes in 

 the air, and acts on water energetically, thus : 



CH 3 COC1 + H 2 O = CH 3 COOH + HC1. 



It is a valuable reagent for testing for alcoholic hydroxyl groups in organic 

 compounds, which may be illustrated by its action on ordinary alcohol, thus: 



CH 3 COC1 + C 2 H 5 OH = CH 3 COOC 2 H 5 + HC1. 



Acetates are thus formed by the replacement of hydrogen of hydroxyl by the 

 acetyl radical. 



Acetic anhydride or acetyl oxide, (CH 3 CO) 2 0, is formed by distilling a 

 mixture of anhydrous sodium acetate and acetyl chloride : 



CH 3 COONa + CH 3 COC1 = (CH 3 CO) 2 O + NaCl. 



It is a colorless liquid with a disagreeable odor, boiling at 137 C., and having 

 a specific gravity of 1.073 at 20 C. It is soluble in about 10 parts of water, 

 the solution decomposing slowly with formation of acetic acid. Like acetyl 

 chloride, it unites with hydroxyl groups in organic compounds, forming ace- 

 tates. This process of making acetates from alcoholic compounds is called 

 acetylization, and is often used in analysis of substances. 



Butyric acid, HC 4 H 7 2 . Among the glycerides of butter those of butyric 

 acid are found ; they exist also in cod-liver oil, croton oil, and a few other fatty 

 oils ; some volatile oils contain compound ethers of butyric acid ; free butyric 

 acid occurs in sweat and in cheese. It may be obtained by a peculiar fermen- 

 tation of lactic acid (which itself is a product of fermentation), and is also 

 generated during the putrefaction of albuminous substances. Butyric acid is 

 a colorless liquid, having a characteristic, unpleasant odor; it mixes with 

 water in all proportions. 



Valeric acid, HC 5 H 9 O 2 (Valerianic avid). This acid occurs in 

 valerian root and angelica root, from which it may be separated ; it 



