734 FATTY ACIDS. [App. 



Tunicata. As prepared from this source it is when pure quite white and 

 usually retains the shape of the tissue. It is unacted upon by any 

 reagent except strong acids and alkalis, and by the action of the former 

 it yields some form of sugar. 



FATS, THEIR DERIVATIVES AND ALLIES. 



THE ACETIC ACID SERIES. 



General formula C n H 3n O 3 (monobasic). 



This, which is one of the most complete homologous series of organic 

 chemistry, runs parallel to the series of monatomic alcohols. Thus formic 

 acid corresponds to methyl alcohol, acetic acid to ethyl (ordinary) 

 alcohol, and so on. The several acids may be regarded as being derived 

 from their respective alcohols by simple oxidation : thus ethyl alcohol 

 yields by oxidation acetic acid : C 2 H 6 O + O 2 = C 2 H 4 O 2 + H 3 O. The 

 various members differ in composition by CH g , and the boiling points 

 rise successively by about 19 C. Similar relations hold good with regard 

 to their melting points and specific gravities. The acid properties are 

 strongest in those where n has the least value. The lowest members of 

 the series are volatile liquids, acting as powerful acids; these succes- 

 sively become less and less fluid, and the highest members are colour- 

 less solids, closely resembling the neutral fats in outward appear- 

 ance. Consecutive acids of the series present but very small differences 

 of chemical and physical properties, hence the difficulty of separating 

 them: this is further increased in the animal body by the fact that 

 exactly those acids which present the greatest similarities usually occur 

 together. 



The free acids are found only in small and very variable quantities 

 in various parts of the body ; their derivatives on the other hand form 

 most important constituents of the human frame, and will be considered 

 further on. 



Formic acid. CHO . OH, 



When pure is a strongly corrosive, fuming fluid, with powerful irri- 

 tating odour, solidifying at 0C., boiling at 100 C., and capable of 

 being mixed in all proportions with water and alcohol. It has been 

 obtained from various parts of the body, such as the spleen, thymus, 

 pancreas, muscles, brain, and blood ; in the latter its presence may be 

 due to the action of acids on the haemoglobin. According to some 

 authors 1 it occurs also in urine. 



1 Buliginsky, Hoppe-Seyler's Med. chem. Mittheilung. Heft. 2, S. 240. Tlmdichum, 

 Journ. of the Chem. Soc. Vol. 8, p. 400. 



