K.STI.MATIOX OF BORIC AflD. ST 



The author and Miller have found that it is quite unnecessary 

 either to evaporate the milk, ignite it. or to use any indicator 

 other than phenol-phthalein ; the method is — to a measured 

 or weighed quantity of milk (10 c.c. saffices) add half its bulk 

 of a fi'5 per cent, solution of phenol-phthalein. and run in alkali 

 till a pink colour appears, boil, and titrate back while still boilint; 



with acid solution till white, and finally with ~ alkali till faintly 



pink. The colour, though faint, is quite distinct, and no attempt 

 should be made to obtain a pronounced pink colour. Add :5i) pii 



cent, of ylvcerol, and continue the titration with r— alkali 

 ■^ 10 



without further heating; subtract, if necessary, the glycerol 



blank, and the alkali used for the final titration multiplied by 



(,)'00fi"2 gives the boric acid. 



Cassal and (ierraiis find that an intense magenta-red colour 

 is produced on treating solutions containing boric acid with 

 curcumin — or ordinary turmeric itself — and oxalic acid, and 

 drying the mixture on the water-bath. The colour is different 

 from that obtained by the application of the ordinary turmeric 

 test for boric acid and the reaction is far more delicate, extremely 

 minute quantities of boric acid being easily detected. The 

 colour is practically permanent for seveial hours — not less than 

 ten or twelve — and fades very gradually on long keeping. The 

 colouring matter is readily soluble in alcohol and ether without 

 alteration, but i.s destioyed by the addition of water in excess. 

 On treatment with alkali an intense blue colour is obtained, 

 which is different from that obtained on treating the '" rose- 

 red " colouring matter formed in the ordinary turmeric test. 

 with alkali. In applying the test for the detection of free or 

 combined boric acid in milk and other food products it is con- 

 venient as a rule to operate on an ash. The ash is treated with 

 a few drops of (1) dilute hydrochloric acid, (2) saturated solution 

 of oxalic acid, and (3) alcoholic solution of curcumin or turmeric. 

 and the mixture dried on the water-bath and taken up with 

 a little alcohol. In cases where the amount of boric acid is 

 very small the substance, the ash of which is to be operated 

 upon, should be made alkaline with solution of barium hydroxide 

 prior to evaporation and incineration. Caustic potash and 

 caustic soda and salts of potassium and sodium in large amounts 

 interfere with tlie formation of the colouring matter. 



They also apply thi^ reaction for the quantitative estimation 

 of boric acid. 



In the case of milk, from 15 to iti grammes are weighed out, 

 transferred to KK) c.c. flask, and made up to 100 c.c. with water. 

 Ten C.I-. (or more, according to circumstances) are transferred 



