302 CONSIDERATION OF CARBON COMPOUNDS. 



435. What is picric acid, and what is it used for? 



436. What relation exists between benzoic acid and oil of bitter 

 almond? 



437. What is the source of amygdaline, and into what substances is 

 it decomposed by emulsine in the presence of water ? 



438. Explain the process for the manufacture of salicylic acid from 

 carbolic acid, and state its properties. 



439. State the general properties of tannins. 



440. From what, and by what processes are gallic and tannic acids 

 obtained ? 



45. ETHERS. 



Constitution. It has been shown that alcohols are hydrocarbon 

 residues in combination with hydroxyl, HO, and that acids are 

 hydrocarbon residues in combination with carboxyl, CO. OH; 

 it has further been shown that carboxyl may be considered as 

 being composed of CO, and hydroxyl HO, and that the term 

 acid radical is applied to that group of atoms in acids which 

 embraces the hydrocarbon residue + CO. If we represent an 

 alcohol radical by AIR, and an acid radical by AcR, the general 



formula of an alcohol is A1R.HO or TT /O, and of an acid, 

 AcRHO or 



Ethers are formed by replacement of the hydrogen of the 

 hydroxyl in alcohols by hydrocarbon residues (or alcohol radicals), 

 and compound ethers or esters are formed by replacement of the 

 hydrogen of the hydroxyl (or carboxyl) in acids by hydrocarbon 

 residues. While alcohols correspond in their constitution to 

 hydrates, ethers correspond to oxides, and compound ethers to 

 salts. For instance : 



Hydrates. Oxides. Acids. Salts. 



KHO = = ^\0 K 2 |\0 HN0 3 = W jf\O KNO 3 = N ^/ 



Potassium hydrate. Potassium oxide. Nitric acid. Potassium nitrate. 



CHc\ f*. C.)Hc \ /-v C W HoO\X-V CqlloOX/-! 



w O p n H f TT 



Ethyl alcohol. Ethyl ether. Acetic acid. Ethyl acetate, or 



acetic ether. 



AlK\ n AlK\ n AcE\ n AcR\ n 



A1RX U H/ U A1RX 



Alcohol. Ether. Acid. Compound 



ether. 



