142 METHODS OF ANALYSIS [Chap. 



disulphid or petroleum ether (b. p. below 60°C.), rubbing the contents of the dish 

 with a glass rod, and filtering the successive portions of the solvent through a dry 

 paper into a second porcelain dish. Evaporate the greater portion of the solvent 

 on a steam bath, allow the remainder to evaporate spontaneously and test the 

 residue as directed above. 



(C) Transfer the residue from the ether extract, obtained as directed above, 

 to a small porcelain crucible by means of a few cc. of ether and allow the solvent 

 to evaporate spontaneously. Cut a hole in a piece of asbestos board sufficiently 

 large to admit about two thirds of the crucible, cover the latter with a small, round- 

 bottomed flask filled with cold water, and heat over a small Bunsen flame until 

 any salicylic acid present has sublimed and condensed upon the bottom of the 

 flask. Test the sublimate as directed above. 



3 Jorissen's Test.^ — Qualitative. 



Dissolve the residue from the ether extract, obtained as directed under 2, or, 

 in case impurities are present, the purified material obtained as directed under 2 

 (a), (b) or (C) in a little hot water. Cool 10 cc. of the solution in a test tube, add 



4 or 5 drops of 10% potassium nitrite solution, 4 or 5 drops of 50% acetic acid and 

 1 drop of 10% cupric sulphate solution, mix thoroughly and heat to boiling. Boil 

 for half a minute and allow to stand for 1-2 minutes. In the presence of salicylic 

 acid a blood red color will develop. 



Colorimetric Method. — Quantitative. 



4 EXTRACTION. 



Pipette a convenient portion of the sample (100 cc. or a volume representing not 

 less than 20 grams of the original sample) or a solution, prepared as in 1 , into a sepa- 

 ratory funnel, make the solution neutral to litmus with dilute hydrochloric acid 

 (1 to 3) and add an excess of concentrated hydrochloric acid equivalent to 2 cc. 

 of acid for each 100 cc. of solution. Extract with 4 separate portions of ether, 

 using for each extraction a volume of ether equivalent to half the volume of the 

 aqueous layer. If an emulsion forms on shaking, this may usually be broken by 

 adding a little (one fifth the volume of the ether layer) petroleum ether (b. p. be- 

 low 60°C.) and shaking again or by centrifugalizing. If an emulsion still persists, 

 allow it to remain with the aqueous layer. If an emulsion remains after the 

 fourth extraction, separate it from the clear ether and the clear aqueous layer 

 and extract it separately with 2-3 small portions of ether. Combine the ether 

 extracts, wash with one tenth their volume of water, allow the layers to separate 

 and reject the aqueous layer. Wash in this way until the aqueous layer after sepa- 

 ration yields a yellow color upon the addition of methyl orange and 2 drops of N/10 

 sodium hydroxid. Distil slowly the greater part of the ether, transfer the remainder 

 to a jjorcelain dish and allow the ether to evaporate spontaneously. If there are 

 no interfering substances present, proceed as directed in 5. If such interfering 

 substances are present, purify the residue by one of the following methods: 



(a) Dry thoroughly the residue in vacuo over sulphuric acid and extract with 

 10 portions of 10-15 cc. each of carbon disulphid or petroleum ether (b. p. below 

 60°C.), rub the contents of the dish with a glass rod and filter the successive portions 

 of the solvent through a dry filter into a porcelain dish. Test the extracted resi- 

 due with a drop of ferric alum solution and, if it gives a reaction for salicylic acid, 

 dissolve it in water and reextract with ether, proceeding as directed above. Dis- 

 til the greater portion of the carbon disulphid or petroleum ether and allow the 

 remainder to evaporate spontaneously. Proceed as directed in 5. 



