with ferric chlorid or calcium chlorid, making alkaline, and filtering. By this means 

 tannin is entirely separated from the product and other substances whose color masks 

 the salicylic acid reaction are often removed. It is sometimes found convenient in the 

 presence of a considerable amount of fat to wash the ether solution, by shaking in a sepa- 

 ratory funnel, with water made alkaline with ammonium hydroxid.a Salicylic acid is thus 

 removed completely, while the fat remains dissolved in the ether. If the excess of 

 ammonia be not too great, evaporate the ammonia solution in a dish over the water bath 

 until all free ammonia has disappeared, and test for salicylic acid with ferric solution as 

 directed above. 



(b) QUANTITATIVE DETERMINATION. 



Extract in a separatory funnel 100 cc of the sample b [in the case of solids and semisolids use 

 the aqueous solution prepared from the sample as described under (a) ] with 75 cc of sul- 

 phuric ether, after the addition of 2 or 3 cc of dilute (1 : 3) sulphuric acid. Separate the 

 clear, aqueous solution, and if any emulsion is present give the separatory funnel a quick, 

 vigorous shake and allow to settle again. If the emulsion is not broken up in this way it 

 may be accomplished by means of a centrifuge or by adding 10 or 15 cc of low boiling point 

 gasoline or petroleum ether and shaking again. 



The clear, aqueous portion is then united with the first, and the ether is poured into 

 another separatory funnel, care being taken that none of the aqueous portion be left with the 

 ether. The aqueous portion is returned to the separatory funnel and again extracted with 

 75 cc of ether, following the same procedure as before. This operation is then repeated 

 twice, making four separate extractions with ether in all. 



In case of special difficulty in breaking up the emulsion in any of the extractions a small 

 amount of ether may be allowed to remain with the aqueous portion rather than the reverse, 

 as it is removed in successive extractions. Wash the combined ether extracts by shaking 

 in a separatory funnel with one-tenth their volume of water (using, however, not less than 

 20 cc of the water at each washing). Care must be taken at each washing to separate the 

 aqueous portion completely from the ether, but none of the ether should be allowed to run 

 into the wash water. In introducing the water into the separatory funnel care should be 

 taken to wash off the stopper and the neck of the funnel to remove any adhering mineral acid. 



Distill slowly the greater part of the ether, transfer the remainder to a porcelain dish, and 

 allow to evaporate spontaneously. Thoroughly dry in a vacuum desiccator c over sulphuric 

 acid, extract the dry residue with ten portions of 10 or 15 cc each of low boiling point gaso- 

 line or petroleum ether, rubbing the contents of the dish with a glass rod or other suitable 

 instrument and transferring the successive portions of solvent to a second porcelain dish. 

 The extracted residue should finally be tested with a drop of ferric alum solution, and if 

 any reaction for salicylic acid be given the residue should be taken up in water, reextracted 

 with ether, and the operation repeated. The gasoline extract is finally allowed to evapo- 

 rate spontaneously. 



Dissolve the residue in a small amount of hot water and dilute to a definite volume. 

 Dilute aliquot portions of the solution and match in Nessler tubes, or with a colorimeter, 

 the color obtained by adding a few drops of dilute ferric chlorid or ferric alum solutions 

 with that of a standard solution of salicylic acid. If a colorimeter be employed, the solution 

 whose color is compared should contain about 1 milligram of salicylic acid in 50 cc. If the 

 color be compared in Nessler tubes without the use of a colorimeter, the solution may advan- 

 tageously contain about 2 milligrams in 50 cc. To 50 cc of the diluted solution add ferric 

 solution until no further color develops. 



a Allen, Commercial Organic Analysis, 2d ed., 4- 188. 



b If the qualitative examination has shown a very large amount of salicylic acid to be present, 50 cc 

 or the aqueous extract of 50 grams of sample will be found sufficient and 40 cc of ether may be employed 

 for its extraction. 



c In examining a substance whose ether extract does not give a color or precipitate with ferric solu- 

 tion, the drying of the residue and its extraction with gasoline may be omitted. The residue may then 

 be transferred by means of warm water directly from the distilling flask to the graduated flask, in 

 which it is made up to a definite volume. Substances interfering with the ferric reaction may often 

 be removed by precipitation with ferric chlorid or lime, as directed at the foot of page 3. 



