52 FOOD ADULTERATION AND METHODS FOR DETECTION. 



the difficulty experienced in the preservation of milk in warm weather 

 has led to the widespread use of chemical preservatives. 



Detection of water. If a lactometer or hydrometer, which can be 

 obtained of dealers in chemical apparatus, be available, the specific 

 gravity of milk will afford some clew as to whether the sample has 

 been adulterated by dilution with water. Whole milk has a specific 

 gravity between 1.027 and 1.033. The specific gravity of skimmed 

 milk is higher, and milk very rich in cream is sometimes lower than 

 these figures. It is understood, of course, that by specific gravity is 

 meant the weight of a substance with reference to the weight of an 

 equal volume of water. The specific gravity of water, therefore, is 

 exactly 1. It is obvious that if water be added to a milk with the 

 specific gravity of 1.030, the specific gravity of the mixture will be 

 somewhat below those figures. 



An indication by means of a hydrometer or lactometer below the 

 figure 1.027 therefore indicates either that the sample in question is a 

 very rich milk or that it is a milk (perhaps normal, perhaps skimmed) 

 that has been watered. The difference in appearance and nature of 

 these two extremes is sufficiently obvious to make use of the lactometer 

 or hydrometer of value as a preliminary test of the purity of milk. 



Detection of color. As previously stated, when milk is diluted by 

 means of water the natural yellowish-white color is changed to a bluish 

 tint, which is sometimes corrected by the addition of coloring matter. 

 Coal-tar colors are usually employed for this purpose. A reaction for 

 these colors is often obtained in the method given below for the detec- 

 tion of formaldehyde. When strong hydrochloric acid is added to 

 the milk in approximately equal proportions before the mixture is 

 heated a pink tinge sometimes is evident if a coal-tar color has been 

 added. 



Detection of formaldehyde. Formaldehyde is the substance most 

 commonly used for preserving milk and is rarely, if ever, added to 

 any other food. Its use is inexcusable and especially objectionable in 

 milk served to infants and invalids. 



To detect formaldehyde in milk 3 or 4 tablespoonfuls of the sample 

 are placed in a teacup with at least an equal amount of strong hydro- 

 chloric acid and a piece of ferric alum about as large as a pinhead, 

 the liquids being mixed by a gentle rotary motion. The cup is then 

 placed in a vessel of boiling water, no further heat being applied, and 

 left for five minutes. At the end of this time, if formaldehyde be 

 pivsent, the mixture will be distinctly purple. If too much heat is 

 applied, a muddy appearance is imparted to the contents of the cup. 



CAUTION. Great care must be exercised in n'<n-kimj n-Uti hydrochloric m-/V, <i* it /'., 

 strongly corrosive. It must not come in contact n-UJi tin- //<>// / r/o///* of fin- operator nor 

 with any metallic vessels and must be greatly diluted with water before it is poured into the 

 sink. 



