\V. \TKKING OF MII.K. 191 



There are two different methods which are easily carried 

 out, those of Hehner and Leach. 



Hchncr 's test for formaldehyde : 



"To 10 cc. of milk in a wide test tube add about half the volume of 

 concentrated commercial sulphuric acid, pouring- the acid carefully down 

 the side of the tube so that it forms a layer at the bottom, without mix- 

 ing with the milk. A violet /.one at the junction of the two liquids indi- 

 cates formaldehyde. The coloration produced depends on the presence 

 of a very small amount of iron. For this reason the ordinary commercial 

 acid used in the Babcock test answers well for this test. However, if an 

 excess of formaldehyde is present in the milk, this test w T ill not indicate 

 the presence of the preservative." 



Leach' s test for formaldehyde : 



"Commercial hydrochloric acid (specific gravity 1.2) containing 2 cc. 

 of 10 % ferric chloride per liter is used as a reagent. Add 10 cc. of the 

 acid reagent to an equal volume of milk in a porcelain casserole, and 

 heat slowly over the free flame nearly to boiling, holding the casserole 

 by the handle, and giving it a rotary motion while heating to break up 

 the curd. The presence of formaldehyde is indicated by a violet color- 

 ation, varying in depth with the amount present. In the absence of 

 formaldehyde, the solution slowly turns brown. By this test 1 part of 

 formaldehyde in 250,000 parts of milk is readily detected before the milk 

 sours. After souring, the limit of delicacy proves to be about 1 part in 

 50,000." 



The porcelain casserole can be obtained at any chemical sup- 

 ply house and the solution as indicated can very easily be made 

 up by any druggist. In place of the gas flame, an alcohol 

 lamp may be used. A word of caution must be mentioned 

 with reference to this test, because it is so delicate. In at least 

 one instance the use of absorbent cotton in a strainer at a good 

 dairy resulted in the finding of formaldehyde in the milk. 

 Investigation showed that the cotton had been sterilized with 

 formaldehyde by the manufacturers. The use of formaldehyde 

 in the tubes of milking machines offers like possibilities for the 

 contamination of milk by this chemical. 



Watering of milk. One of the more common sophistications 

 of milk is the addition of water. Such a practice is not only a 

 pecuniary fraud but it both lowers the nutritive value and 

 may prove at times to be a menace to health, as discussed in 

 Chapters III and V. 



