MONOBASIC FATTY ACIDS. 507 



to the air it decomposes and shows then an acid reaction. Lead 

 oleate is soluble in ether, lead palmitate and lead stearate are 

 not. 



The official oleates of mercury, quinine, veratrine, atropine, and 

 cocaine are obtained by dissolving the yellow mercuric oxide, quinine, 

 veratrine, atropine, or cocaine in oleic acid. 



Dissociation of formic acid and its homologues. In Chapter 15 it is 

 stated that the " strength " or relative activity of acids and'bases is propor- 

 tional to their degree of dissociation in solution. Organic acids in solution are 

 dissociated only to a small degree and are much " weaker " than such mineral 

 acids as hydrochloric, nitric, and sulphuric, which are almost completely disso- 

 ciated in very dilute solutions. The following table shows the percentage of 

 molecules dissociated in aqueous solutions containing the molecular weight in 

 grams of the respective acids diluted to 8 liters : 



Further dilution does not increase the percentage of dissociation very much. 

 For example, the molecular weight of acetic acid in 16 liters of solution disso- 

 ciates only to the extent of 1.673 per cent., whereas in a similar solution of 

 hydrochloric acid the dissociation is 95.5 per cent. Formic acid dissociates 

 more than the others of the series, and is, therefore, the strongest acid of the 

 series. The salts of organic acids are dissociated much more than the acids 

 are. Thus, in a normal solution of acetic acid only 0.4 per cent, of the molecules 

 are dissociated, while in normal solutions of sodium and potassium acetate 

 53 per cent, and 64 per cent, respectively, of the molecules are dissociated. 



QUESTIONS. What is the constitution of organic acids, what group of 

 atoms is found in all of them, and how does an alcohol radical differ from an 

 acid radical? Give some processes by which organic acids are formed in nature 

 or artificially. Mention the general properties of organic acids. Which series 

 of acids is known as fatty acids, and why has this name been given to them ? 

 Mention names, composition, and occurrence in nature of the first five mem- 

 bers of the series of fatty acids. By what processes may formic acid be ob- 

 tained, and what are its properties? Describe the processes of manufacturing 

 acetic acid from alcohol and from wood. What is vinegar, and what is glacial 

 acetic acid ? Give tests for acetic acid and for acetates. Describe the pro- 

 cesses for making the acetates of potassium, zinc, iron, lead, and copper, and 

 also of Goulard's extract and lead-water ; state their composition and proper- 

 ties. Where and in what form of combination is oleic acid found in nature, 

 and what are its properties ? 



