108 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



(b) FIRST METHOD OF DETECTION. 



To about 5 cc of the distillate described above add 2 or 3 drops of a 1 per cent aque- 

 ous solution of phenol; mix and carefully pour it on about the same amount of con- 

 centrated sulphuric acid in a test tube, holding the tube so that the solutions will not 

 mix. The presence of one part of formaldehyde in 100,000 parts is indicated by the 

 formation of a crimson color at the plane of union of the solutions. If the formalde- 

 hyde be present in greater quantity, a white turbidity, or a light-colored precipita- 

 tion, will be formed above the coloring. 



If organic matter is distilled over, the charring of it by the sulphuric acid may be 

 mistaken for a trace of formaldehyde; but, on allowing the test to stand for twelve 

 hours, the coloration, if due to formaldehyde, will become a whitish turbidity instead 

 of the dark color which appears if due to the charring of organic matter. Some other 

 aldehydes will give the same result, and it is, therefore, not conclusive. 



(c) SECOND METHOD OF DETECTION.* 



Add about 5 cc of the distillate obtained under (a) to an equal volume of pure 

 milk in a porcelain casserole, and about 10 cc of concentrated hydrochloric acid con- 

 taining 1 cc of 10 per cent ferric chlorid solution to each 500 cc of acid. Heat to 80 

 or 90 directly over the gas flame, holding the casserole by the handle and giving it 

 a rotary motion to break up the curd. A violet coloration indicates formaldehyde. 



(d) THIRD METHOD OF DETECTION. 



Dissolve 1 gram of phenylhydrazin hydrochlorid and 1.5 grams of sodium acetate 

 in 10 cc of water. To 1 cc of distillate obtained as directed in (d) add 2 drops of 

 reagent and 2 drops of sulphuric acid. If formaldehyde is present, a green color will 

 be produced. 



2. DETECTION OF SULPHUROUS ACID. 



Prepare samples as directed under 1 (a), and boil 20 cc of the distillate after the 

 addition of a few drops of bromin or iodin solution. If it is decolorized quickly, test 

 for sulphuric acid with barium chlorid solution. 



If sulphurous acid or sulphite is present, determine it quantitatively as directed 

 under wine (page 90). 



3. DETECTION OF SALICYLIC ACID. 



If the material be a solid or semisolid, macerate 200 to 300 grams in a mortar with 

 about 400 cc of water made slightly alkaline with sodium or potassium hydroxid, and 

 strain through a cotton bag. Acidify the nitrate with dilute (1:3) sulphuric acid, 

 and extract by shaking with about 30 cc of chloroform or ether. b Separate from the 

 water with a separatory funnel. If a clear solution is obtained, place the chloroform 

 or ether in a small porcelain dish and evaporate at a low temperature. If an emul- 

 sion is formed and a clear solution will not separate out on standing, whirling in a 

 Babcock milk tester or some other centrifugal machine will usually give the desired 

 clear solution. Take up the residue in the porcelain dish with 3 or 4 cc of hot water 

 and divide into two portions, one for salicylic acid and the other for saccharin. 



In the case of materials containing large amounts of extractive matter, and those 

 from which the water solution can not be separated from the solid matter by strain- 

 ing, it may be found necessary to separate them by distillation, though straining is 

 always preferable. In such cases acidify the macerated material with phosphoric 

 acid, and transfer to a distilling flask, with a very short neck and wide mouth. An 

 Erlenmeyer flask with inside diameter of mouth l\ inches is a good shape. The 



Leach, Twenty-ninth An. Rep. Mass. Board of Health, 1897, p. 658. b See appendix, page 160. 



