PRESERVATIVES. 185 



(another characteristic smell) ; this may be converted into 

 aniline, diazotised and condensed with /3-naphthol (red colour). 



(c) Evaporate a little of the solution to dryness, add 2 c.c. 

 of aniline and 0"02 gramme rosaniline hydrochloride, and boil 

 for twenty minutes ; a blue colour is produced if benzoates are 

 present. 



(r7) Evaporate a little of the solution to dryness, add a little 

 gallic acid and 1 c.c. sulphuric acid ; if benzoates are present 

 anthragallol is produced, which, on dilution and making alkaline, 

 gives a red colour passing to brown. 



/i-naphthol is best detected by taking advantage of its easy 

 condensation with tetrazonium salts in faintly acid solution 

 to form dark red compounds. 



The author and Miller test as follows : — To 1 gramme of 

 benzidine add 4 c.c. strong HCl and about 60 or 70 c.c. of water ; 

 keep this solution cool, and add little by little 1 gramme sodium 

 nitrite dissolved in about 25 c.c. of water, cooling, and shaking 

 well between each addition. When all the nitrite has been 

 added nearly neutralise, usinj^ phenolphthaleiii as indicator. 

 To a few c.c. of milk add a little of this solution ; if ,S-naphthol 

 is present a red colour will be produced. Do not make alkaline, 

 as milk itself i,avc's a brownish-red in alkaline solution. 



As a confirmatory test, a diazotised solution of phenylhvdrazine 

 may be used, which gives a red colour in alkaline solution with 

 ^-naphthol, but no colour with milk. 



If the milk is extracted with chloroform, and the chloroform 

 heated with caustic potash for a few minutes, a deep blue colour 

 indicates the presence of /S-naphthol. 



Fluorides are thus detected in the ash of milk. At least 

 •25 c.c. of milk should be taken, and the ash treated in a platinum 

 basin with a little strong sulphuric acid. Over the top of the 

 basin a watch-glass coated with bees' wax, through which a 

 few lines are scratched, is placed, and a piece of ice or some cold 

 water is put into the concave depression. The basin is then 

 gently warmed and the watch-glass exposed to the action of the 

 fumes evolved for ten minutes. In the presence of fluorides 

 it is seen that the glass has been etched, after removal of the 

 wa.x. If a drop of water is placed on the wax, away from the 

 lines scratched through it, a white film of silica will be formed 

 on its surface if fluosilicates be present. If fluoborates 

 be present, this drop of water will give a boric acid reaction ; in 

 the presence of fluoborates both a fluoride and a boric acid 

 reaction are given by the ash of the milk. 



0. and C. Hehner have pointed out that when there is much 

 boric acid in relation to the fluoride present, the test for fluorides 

 applied directly to the ash fails. The milk should be made 



