262 METHODS OF ANALYSIS [Chap. 



18 ALC O HDL.— TE NTATIVE. 



Dilute 50 cc. of the extract, measured at 20°C., with water to about 200 cc, allow 

 the mixture to stand until the oil separates in a clear layer at the top, or centrifugal- 

 ize, then make up to the mark, using the lower meniscus of the oil. Pour the mixture 

 into a dry Erlenmeyer flask containing 5 grams of light magnesium carbonate, 

 stopper, shake well and filter quickly through a large, dry, folded filter. Intro- 

 duce a 150 cc. aliquot of the filtrate, measured at 20°C., into a 300-500 cc. distilla- 

 tion flask, attach the flask to a vertical condenser and distil almost 100 cc. Com- 

 plete the volume of the distillate to 100 cc. at 20''C., mix well and determine the 

 specific gravity at -p-^ • Ascertain the corresponding per cent of alcohol by volume 

 from XVI, 5 and multiply the result thus obtained by 2f to obtain the percentage 

 of alcohol by volume in the original sample. 



19 GLYCEROL.— TENTATIVE. 



Proceed as directed under 3. 



LEMON AND ORANGE OILS. 



20 By Polarization. {Mitchell Method)— Tentative. 



Without diluting polarize the extract at 20°C. in a 200 mm. tube. Divide the 

 reading in degrees Ventzke by 3.2 in the case of lemon extract and by 5.2 in the 

 case of orange extract; in the absence of other optically active substances, the re- 

 sult will be the percentage of oil by volume. A small amount of cane sugar is occa- 

 sionally present; if so, determine as directed under 28 and correct the reading 

 accordingly. 



21 By Precipitation. {Mitchell Method) — Tentative. 



Pipette 20 cc. of the extract into a Babcock milk bottle, add 1 cc. of hydrochloric 

 acid (1 to 1), then 25-28 cc. of water previously warmed to 60°C., mix, let stand 

 in water at 60°C. for 5 minutes, centrifugalize for 5 minutes, fill with warm water 

 to bring the oil into the graduated neck of the flask, again centrifugalize for 2 min- 

 utes, place the flask in water at 60°C. for a few minutes and note the per cent of oil 

 by volume. If oil of lemon is present in amounts over 2%, add 0.4% to the per- 

 centage of oil noted to correct for the solubility of the oil. If less than 2% and 

 more than 1% is present, add 0.3% for this correction. 



When the extract is made in accordance with the U. S. P., the results by the 

 methods given under 20 and 21 should agree within 0.2%. 



To obtain the per cent by weight from the per cent by volume, as found by either 

 of these methods, multiply the volume percentage by 0.86 in the case of lemon ex- 

 tracts, and by 0.S5 in the case of orange extracts, and divide the result by the specific 

 gravity of the original extract. 



TOTAL ALDEHYDES. 

 Chaxie Method*. — Tentative. 



22 REAGENTS. 



(a) Aldehyde-free alcohol. — Allow 95% alcohol by volume, containing 5 grams 

 of meta-phenylendiamin hydrochlorid per liter, to stand for 24 hours with fre- 

 quent shaking. (Nothing is gained by previous treatment with potassium hy- 

 droxid.) Boil under a reflux condenser for at least 8 hours, longer if necessary, 

 allow to stand overnight and distil, rejecting the first 10 and the last 5 per cent 



