ADDITION OF ANTISEPTICS 63 



milk are mixed with milk of lime, evaporated and 

 ignited ; the ash is dissolved in a very little concentrated 

 hydrochloric acid ; the carbon is filtered out, the filtrate 

 is made slightly alkaline and evaporated to dryness. 

 This salt is treated with a little turmeric tincture and 

 with some very dilute sulphuric acid and is evaporated 

 in a water bath. If boric acid is present, the mass is 

 colored a distinct cherry red. 



[Leffmann 8 gives the following method: "A few 

 drops of the sample are mixed with a drop of hydro- 

 chloric acid and a drop of strong alcoholic solution of 

 turmeric, evaporated to dryness at a gentle heat, and a 

 drop of ammonium hydroxide added to the residue when 

 cold. A dull green stain shows that boric acid is pres- 

 ent/' 



Richmond 9 offers this method : " To a little milk add 

 a few drops of phenolphthalein, and sodium hydroxide 

 solution, drop by drop, till a faint pink color is pro- 

 duced; place some of the milk in two test tubes, dilute 

 one with an equal volume of water, and the other with a. 

 neutral 50 per cent, solution of glycerin ; in the absence 

 of boric acid the two tubes will have almost the same 

 color, in its presence the glycerin tube will be the 

 lighter, and usually white. ' ' L.P. ] 



b. Salicylic acid in a quantity equivalent to 0.04 per 

 cent, can prevent the souring of milk for 36 hours, even 

 when the milk remains at 18 C. It is very hard to 

 dissolve and has not been extensively used to preserve 

 milk. 



Salicylic acid has the effect of checking digestion and, 

 with some persons, it may cause irritation of the kid- 

 neys ; particularly for children, salicylic acid should be 



8 Analysis of Milk and Milk Products. 



9 Laboratory Book of Dairy Analysis. 



