MIXED COMPOUNDS 67 



The product is chloral, an oily liquid boiling at 97° C. When 

 boiled with alkalies, it breaks down and yields chloroform. It 

 possesses the characteristic property of uniting with water, 

 forming a crystalline compound known as chloral hydrate 

 CCI3— CHO . H2O. The evidence seems to point to the con- 

 clusion that in chloral hydrate we have a compound of the 

 constitution, not of an aldehyde, but of a dihydroxy compound, 

 viz. CCI3— CH(0H)2. This is a marked exception to the 

 general fact before referred to, that compounds containing two 

 hydroxyl groups united to one carbon do not exist. 



Chloral hydrate forms clear monoclinic prisms melting at 

 57° C. It is a very valuable and commonly used soporific 

 and anaesthetic. 



Halo gen-acids 



Chlor-acetic Acids. — As illustrations simply of the halogen- 

 acids we may mention the halogen substitution products of 

 acetic acid formed by introducing first one, then two, and finally 

 three chlorine atoms in acetic acid. 



CH3 - COOH + CI2 -> CH2CI - COOH + HCl 



Acetic acid Mono-chlor-acetic acid 



CH2CI - COOH + CI2 "> CHCI2 - COOH + HCl 



Di-chlor-acetic acid 



CHCI2 - COOH + CI2 -> CCI3 - COOH + HCl 



Tri-chlor-acetic acid 



This reaction takes place with chlorine alone in the direct sun- 

 light or by means of iodine tri-chloride, ICI3, without sunlight. 

 These three compounds have been of the greatest importance 

 in establishing our ideas of substitution. All of these substi- 

 tuted acetic acids are strongly acid, even more so than acetic 

 acid itself. 



HYDROXY-ACIDS 



The polysubstitution products in which both hydroxyl and 

 carboxyl groups are present contain some very important com- 

 pounds which have direct connection with agriculture. All of 



