APPENDIX. 



Propionic Acid. C 3 H 5 O.OH. 



This acid closely resembles the preceding one. It possesses a very sour taste and 

 pungent odor; it is soluble in water, boils at 141 C., and may be separated from 

 its aqueous solution by excess of calcic chloride. 



It occurs in small quantities in sweat, in the contents of the stomach, and in 

 diabetic urine when undergoing fermentation. It is similarly produced, mixed, 

 however, with other products, during alcoholic fermentation, or by the decompo- 

 sition of glycerin. It partially reduces silver nitrate solution on boiling. 



Butyric Acid. C 4 H 7 O.OH. 



An oily, colorless liquid, with an odor of rancid butter, soluble in water, alcohol, 

 and ether, boiling at 162 C. Calcic chloride separates it from its aqueous solution. 



Found in sweat, the contents of the large intestine, feces, and in urine. It oc- 

 curs in traces in many other fluids, and is plentifully obtained when diabetic urine is 

 mixed with powdered chalk and kept at a temperature of 35 C. It exists as a 

 neutral fat in small quantities in milk. 



Valerianic Acid. C 5 H 9 O.OH. 



An oily liquid, of penetrating odor and burning taste ; soluble in 30 parts of 

 water at 12 C. ; readily soluble in alcohol and ether. Boils at 175 C. ; possesses, 

 in free and combined form, a feeble right-handed rotation of the plane of polariza- 

 tion. 



It is found in the solid excrements, and is formed readily by the decomposition, 

 through putrefaction, of impure leucin, ammonia being at the same time evolved ; 

 hence its occurrence in urine when that fluid contains leucin, as in cases of acute 

 atrophy of the liver. 



Caproic Acid. C 6 H n O.OH.. 



Caprylic Acid. C 8 H 15 O.OH. 



Capric (Rutic) Acid. C 10 H 19 O.OH. 



These three occur together (as fats) in butter and are contained in varying pro- 

 portions in the feces from a meat diet. The first is an oily fluid, slightly soluble in 

 water ; the others are solids and scarcely soluble in water ; they are soluble in all 

 proportions in alcohol and ether. They may be prepared from butter, and sepa- 

 rated by the varying solubilities of their barium salts. 



Laurostearic Acid. C 12 H., 3 O.OH. 

 Myristic Acid. C U H 27 O.OH. 



These occur as neutral fat in spermaceti, in butter, and other fats. They pre- 

 sent no points of interest. 



Palmitic Acid. C 16 H 31 OH. 

 Stearic Acid. C ]8 H 35 O.OH. 



These are solid, colorless when pure, tasteless, odorless crystalline bodies, the 

 former melting at 62 C., the latter at 69.2 C. In water they are quite insoluble ; 

 palmitic acid is more readily soluble in cold alcohol than stearic ; both are readily 

 dissolved by hot alcohol, ether, or chloroform. Glacial acetic acid dissolves them 

 in large quantity, the solution being assisted by warming. They readily form soaps 

 with the alkalies, also with many other metals. The varying solubilities of their 

 barium salts aiford the means of separating them when mixed ; l this may also be 

 applied to many others of the higher members of this series. 



These acids in combination with glycerin (see below), together with the analo- 

 gous compound of oleic acid, form the principal constituents of human fat. As 

 salts of calcium they occur in the feces and in " adipocere." and probably in chyle, 

 blood, and serous fluids, as salts of sodium. They are found in the free state in 

 decomposing pus, and in caseous deposits of tuberculosis. 



The existence of margaric acid intermediate to the above two is not now admitted, since 

 Heintz 2 has shown that it is really a mixture of palmitic and stearic acids. Margaric acid pos- 

 sesses die anomalous melting-point of 59.9 C A mixture of 60 parts stearic and 40 of palmitic 

 acid melts at 60.3 



1 Heintz, Annal. d. Phys. u. Chem., Bd. xclii., S. 588. 8 Op. cit. 



