BORIC ACID. 109 1 



Boric acid is detected by acidifying the ash slightly with 

 hydrochloric acid and dipping a piece of turmeric paper into- 

 the solution ; on drying, this will assume a pinkish-brown color- 

 ation, turned a very dark green almost black on moistening 

 with a solution of sodium bicarbonate. Cribb and Arnaud pre- 

 pare turmeric paper by boiling 2 grammes of turmeric and 

 2 grammes of tartaric acid with 80 per cent, alcohol till the latter 

 is dissolved, and soaking strips of filter paper in this solution. It 

 is very delicate, and should be kept in the dark. Another test 

 is to moisten the ash with dilute sulphuric acid and add strong 

 alcohol; if boric acid be present, the alcohol will burn with a 

 greenish flame on applying a match. 



Boric acid may also be detected in the milk direct, by acidi- 

 fying with hydrochloric acid, and dipping the turmeric paper 

 in the serum. 



Another simple test for the presence of boric acid consists in 

 putting about J oz. of milk in a glass, adding half its bulk of 

 phenol-phthalein, and dilute caustic soda solution drop by drop, 

 with constant stirring, till a faint permanent pink colour is 

 produced. Some of the pink-coloured milk is poured into 

 two test tubes. To one tube is added an equal bulk of water, 

 and to the other an equal bulk of a neutral mixture of 1 part 

 pure glycerol and 1 part water. In genuine milk both tubes 

 remain pink, and the colours are practically identical, but in 

 the presence of boric acid the water tube becomes darker in 

 tint, and the glycerol tube much lighter usually quite white. 



If boric acid be present, 25 to 50 grammes of milk should be 

 taken for estimation. After addition of about 0-2 gramme caustic 

 soda, the milk is evaporated and charred thoroughly by ignition ; 

 the residue is extracted by dilute acetic acid, and washed well 

 with as small a quantity of water as possible ; the solution is 

 filtered into a small flask to which a condenser is fitted, and 

 distilled to dryness into about 10 c.c. of strong ammonia ; eight 

 successive portions of 10 c.c. each of methyl alcohol are added 

 and distilled off. 



About 1 gramme of lime is ignited in a capacious platinum 

 basin in a muffle at the highest temperature attainable, and the 

 basin and lime weighed. The ammoniacal distillate is now added 

 and the liquid evaporated on the water-bath ; the basin is again 

 ignited in a muffle and weighed. The increase of weight repre- 

 sents the boric anhydride. 



Hehner prefers the use of a measured quantity cf sodium 

 phosphate solution of known strength for fixing the boric acid 

 instead of ammonia and lime. He distils directly into the 

 sodium phosphate solution, evaporates and ignites cautiously. 

 The weight of the residue of pyro -phosphate obtained from an 



