OXIDATION PRODUCTS OF ALCOHOLS 43 



also that the intermediate product above is unknown leads to 

 the view previously referred to (p. 40) that when two hydroxyl 

 groups are united to one carbon an unstable compound is 

 formed which loses water, yielding a stable product. 



Formic aldehyde or, as it is better known, formaldehyde is a 

 common disinfectant and germicide. It is ordinarily used in 

 the form of a 40 per cent water solution under the name of 

 formalin. It is used extensively to disinfect after sickness, and 

 as a germicide in connection with numerous plant diseases such 

 as potato scab, oat smut, etc. It is also used as a food preserv- 

 ative and to preserve anatomical or biological specimens. 

 One of the most common uses as a food preservative has been 

 in preserving milk. Milk so preserved is especially injurious 

 to infants and is strictly prohibited by all health and pure food 

 regulations. The compound is a gas, and when used as a dis- 

 infectant in case of sickness it is generally freshly prepared in 

 this form. The formaldehyde gas is usually generated by pour- 

 ing ordinary formalin upon potassium permanganate. The 

 permanganate acts violently upon the formaldehyde, oxidizing 

 part of it while the heat of the reaction volatilizes the greater 

 part, which goes off as a gas rapidly penetrating all parts of a 

 room. The formalin is also often sprinkled on a hanging sheet, 

 when vaporization of the formaldehyde occurs. When methyl 

 alcohol is burned with a small amount of air, or when a mixture 

 of air and methyl alcohol vapor is passed over heated copper, 

 formaldehyde is the result. This principle is used in making 

 alcohol lamps which produce formaldehyde. The odor observed 

 when a methyl alcohol lamp is blown out is due to formaldehyde. 

 It has a sharp, penetrating, suffocating odor. 



The most important fact in regard to formaldehyde, agricul- 

 turally considered, is its biological relation to the synthesis of 

 carbohydrates in plants from carbon dioxide and water. For- 

 maldehyde may be formed from these two simple compounds, 

 and we may represent the reaction empirically as follows : 



CO2 + H2O -> H-CHO + O2 



