60 DETDCTION OF PRESERVATIVES. 



P'or this reason improved methods for detecting these 

 substances are given below. 



I. BORAX AND BORIC ACID. 



For qualitative tests about lOO c. c. of milk are made 

 alkaline with milk of lime, evaporated to dryness and in- 

 cinerated. The resulting carbon need not be completely 

 burned. The heating is stopped as soon as intumescence 

 ceases. The ash is dissolved in the least possible amount 

 of hydrochloric acid ; filtered off from the carbon ; evap- 

 orated to dryness ; and the excess of HCl completely 

 driven off. The resulting white crystalline residue is 

 treated with a few drops of a tincture of tumeric and very 

 dilute hydrochloric acid and dried on a water bath. The 

 presence of the slightest trace of boric acid gives to the 

 dry residue a beautiful vermillion or cherry red color 

 (Meissel). By the described method it is possible to de- 

 tect with certainty o.ooi to 0.0005 gram of boric acid in 

 the ash or o.ooi to 0.002 per cent in the milk. 



To render the milk alkaline, lime water is preferable 

 to the caustic alkalies because, in fusing, the latter are 

 liable to cover over particles of unburned organic matter 

 and make the conversion to ash difficult. Only very dilute 

 hydrochloric acid must be used in the final evaporation 

 of the crystalline residue in testing for boric acid since 

 the concentrated acid itself gives with tumeric tincture a 

 red color. The coloration produced by boric acid is dis- 

 tinguished from that produced by hydrochloric acid by 

 the fact that it does not disappear by treatment with water 

 in the cold, but only after long boiling. The color caused 

 by hydrochloric acid disappears as soon as it is diluted 

 with water. The acid is easily soluble in alcohol and a 

 trace of it in alcoholic solution colors the flame of the 

 Bunsen burner an intense green. With alcohol, boric 



