112 ESTIMATION OF TOTAL SOLIDS AND ASH. 



without further heating ; subtract, if necessary, the glycerol 

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

 0-0062 gives the boric acid. 



In place of 30 per cent, of glycerol 2 per cent, of mannitol 

 may be used, or even 3 to 5 per cent, of manna, as pointed out 

 by L. E. lies. 



Cassal and Gerrans 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 several 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 is destroyed 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 the formation of the colouring matter. 



They also apply this reaction for the quantitative estimation 

 of boric acid. 



In the case of milk, from 15 to 20 grammes are weighed out, 

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

 Ten c.c. (or more, according to circumstances) are transferred 

 to a porcelain dish and mixed with 15 to 20 grammes of purified 

 sand (obtained by igniting " silver sand," boiling this with 

 25 per cent, hydrochloric acid, and washing thoroughly and 

 drying). The use of a medium such as sand is essential in order 

 to secure intimate and complete contact between the reacting 

 substances at the drying point which is the point of reaction. 

 The mixture is made alkaline with barium hydroxide, and 

 evaporated to dryness. Two c.c. of a 1 per cent, alcoholic solu- 

 tion of curcumin are added, and the mixture evaporated again 



