70 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



Hog's Lard. Mutton Fat. Human Fat. 



Carbon .... 79.098 78.996 79.000 



Hydrogen .... 11.146 11.700 11.416 



Oxygen .... 9.756 9.304 9.584 



100.000 100.000 100.000 



38. The saponification of these fatty substances gives rise to the production 

 of the Margaric, Stearic, and Oleic acids, and of the base known as Glycerine. 

 Margaric acid is a solid white substance, destitute of smell or taste, which 

 crystallizes from a hot alcoholic solution in groups of very delicate nacreous 

 needles, that under the microscope appear interlaced like tufts of grass j it melts 

 at the temperature of 133; and when further heated, it decomposes and be- 

 comes" inflammable. Its alcoholic solution has a slightly acid reaction with 

 litmus-paper. Stearic acid closely resembles the preceding; but it is less solu- 

 ble in hot alcohol, so that when both are dissolved together, it is the first to 

 crystallize as the alcohol cools, and its crystals have the form of elongated 

 lozenge-shaped plates. Its melting-point is 167; and its alcoholic solution has 

 a sufficiently powerful acid reaction to dissolve the alkaline carbonates. Oleic 

 acid, like olein, is liquid at ordinary temperatures, and is a limpid oily fluid, 

 having neither taste nor smell, and exerting no action upon litmus. In this 

 state, when freely exposed to the atmosphere, it absorbs twenty times its volume 

 of oxygen, without giving off carbonic acid, and becomes changed into a thicker 

 fluid which reddens litmus; so that oleic acid usually exhibits this reaction, un- 

 less special care have been taken to obtain it in a state of purity. When cooled 

 down to about 43, however, oleic acid solidifies into a hard white crystalline 

 mass, which remains unaffected by exposure to the atmosphere. It is soluble 

 in alcohol at ordinary temperatures ; but crystallizes out of this solution in long 

 needles, when it is exposed to extreme cold. The following table of the atomic 

 constitution of these acids will assist in showing their mutual relations : 



Stearic. Margaric. Oleic. 



Carbon v * ; > -.'* -.. -j ;; *'. j\- ':..< .',' 68 34 36 



Hydrogen .* - ' V mt 'i'6.-r. ,. V- .> 66 33 33 



Oxygen f ' t * . 'v ^ ., r. ' >.., ' . , 533 



Water , ;; : . " t '. ' ,. ': .;" < ^".' / ., :. 211 



Thus it appears that Stearic acid is the equivalent of two proportionals of 

 Margaric acid, minus 1 eq. of oxygen; and as it is easy to convert the former into 

 the latter by dry distillation, there is every probability that stearic acid is formed 

 in the living body at the expense of the margaric acid, which may be taken in 

 as a constituent of vegetable food. Further, a relation between the Margaric 

 and Oleic acids is indicated by the fact that, when the latter is exposed to the 

 action of oxygen at an elevated temperature, it becomes converted into an acid 

 whose composition is represented by the formula 34C, 33H, 50; whilst the 

 former, when treated with peroxide of lead, so as to be made to undergo further 

 oxidation, is converted into an acid whose composition is represented by the 

 formula 34C, 33H, 40 -f HO; so that these two compounds appear to present 

 different grades of oxidation of one and the same radical. 



39. The substance known as Glycerine is produced in the act of saponifying 

 the ordinary fats of the body of man and of most other animals ; and has been 

 commonly regarded as the base with which the fatty acids are united to form 

 them. It has not been found possible, however, to reproduce margarin, stearin, 

 or olein, by combining their respective acids with glycerine; and there are 

 moreover, adequate reasons for considering that the real base of the fats is a 

 compound having the composition 3C, 2H, 0, whilst glycerine is formed by 

 60, 7H, 50, and that two equivalents of the former are converted into one of 



