6 



DETECTION AND DETERMINATION OF ALCOHOLS, ETC. 



to detect 0.01 per cent in 80 per cent ethyl alcohol. Potassium per- 

 manganate may be substituted for chromic acid in this oxidization, but 

 the sensitiveness of the reaction for aqueous solutions when using 

 this reagent is then only about 1 part in 4,000. For the determination 

 of methyl alcohol the same principles and method given under ethyl 

 alcohol apply. 



FORMIC ACID. 



The detection and determination of formic acid in food products is 

 becoming of increasing importance, not only because of the proposed 

 use of this acid as a preservative but also because it has been found 

 to be one of the products of the fermentative action of bacteria and 

 yeasts on carbohydrates. Fen ton l has shown that carbonic and for- 

 mic acids in aqueous solution may be reduced to formaldehyde by 

 the action of magnesium. The reduction of formic acid has been 

 studied in this laboratory to determine its sensitiveness, and certain 

 other metals have been found to give the same reduction. The for- 

 mation of formaldehyde from carbon dioxid by these metals is of con- 

 siderable theoretical importance; but, in the practical method of test- 

 ing for formic acid, as proposed here, there is no danger of confusing 

 this acid with carbonic acid, as to obtain detectable quantities of 

 formaldehyde from carbon dioxid it is necessary to cause this gas to 

 act on the metal for several hours. 



If a suspected solution is acidified with phosphoric acid and then 

 distilled the amount of carbon dioxid found in the distillate is not 

 sufficient in amount to give detectable quantities of formaldehyde 

 when reduced by metals for any reasonable time. In the following 

 table the action of various metals on 1 per cent and 0.1 per cent 

 formic acid solutions is given, the reduction to formaldehyde being 

 indicated as positive and negative: 



The reduction of formic acid by the action of various metals. 



i J. Chem. Soc. (Lond.), 1907, 91: 687. 



