244 METHODS OF ANALYSIS [Chap. 



8 ESTERS.-TENTATIVE. 



Measure 200 cc. of the sample into a distillation flask, add 25 cc. of water and 

 distil slowly 200 cc, using a mercury valve to prevent loss of alcohol. Exactly 

 neutralize the free acid in 50 cc. of the distillate with N/10 alkali, add a measured 

 excess of 25-50 cc. of N/10 alkali, and either boil for an hour under a reflux con- 

 denser, cool and titrate with N/10 acid, or allow the solution to stand overnight 

 in a stoppered flask with the excess of alkali, heat with a tube condenser for 30 min- 

 utes at a temperature below the boiling point, cool and titrate. Calculate the 

 number of cc. of N/10 alkali used in the saponification of the esters as ethyl acetate; 

 1 cc. of N/10 alkali is equivalent to 0.0088 gram of ethyl acetate. Run a blank using 

 water in place of the distillate and make any necessary correction. 



ALDEHYDES— TENTATIVE. 



9 KBAGENTS. 



(a) Aldehyde-free alcohol. — Redistil 95% alcohol over sodium or potassium hy- 

 droxid, then add 2-3 grams per liter of meta-phenylendiamin hydrochlorid, digest 

 at ordinary temperature for several days (or reflux on a steam bath for several 

 hours) and then distil slowly, rejecting the first 100 cc. and the last 200 cc. of the 

 distillate. 



(b) Sulphite-fuchsin solution. — Dissolve 0.50 gram of pure fuchsin in 500 cc. of 

 water, then add 5 grams of sulphur dioxid dissolved in water, make up to 1 liter 

 and allow to stand until colorless. This solution does not keep indefinitely; there- 

 fore, prepare in small quantities and keep at a low temperature. 



(C) Standard acetaldehyde solution. — Prepare according to the directions of Vasey^ 

 as follows : Grind aldehyde ammonia in a mortar with anhydrous ether and decant 

 the ether. Repeat this operation several times, then dry the purified salt in a 

 current of air and finally in vacuo over sulphuric acid. Dissolve 1.386 grams of this 

 purified aldehyde ammonia in 50 cc. of 95% alcohol by volume, add 22.7 cc. of 

 N/1 alcoholic sulphuric acid, then make up to 100 cc. and add 0.8 cc. of alcohol 

 for the volume of the ammonium sulphate precipitate. Allow the mixture to stand 

 overnight and filter. This solution contains 1 gram of acetaldehyde in 100 cc. and 

 will retain its strength. 



The standard found most convenient for use is 2 cc. of this strong aldehyde 

 solution diluted to 100 cc. with 50% alcohol by volume. One cc. of this solution 

 is equivalent to 0.0002 gram of acetaldehyde. This solution should be made up 

 fresh every day or so, as it loses strength. 



10 DETERMINATION. 



Determine the aldehyde in the distillate, prepared as directed under 8. Dilute 

 5-10 cc. of the distillate to 50 cc. with aldehyde-free alcohol 50% by volume, add 

 25 cc. of the sulphite-fuchsin solution and allow to stand for 15 minutes at 15°C. 

 The solutions and reagents should be at 15°C. when they are mixed. Prepare 

 standards of known strength and blanks in the same way. The comparison 

 standards found most convenient for use contain 0.0001, 0.0002, 0.0004, 0.0005 and 

 0.0006 gram of acetaldehyde. 



FURFURAL.— TENTATIVE. 



11 REAGENTS. 



(a) Standard furfural solution. — Dissolve 1 gram of redistilled furfural in 100 

 cc. of 95% alcohol by volume. Standards are made by diluting 1 cc. of this solu- 



