BORIC ACID AND BORATES 83 



N 

 reaction. Each cubic centimetre of — iodine solution absorbed 



equals 0.0015 grm. of formaldehyde. 



Monier-WilUams, in a report to the Local Government 

 Board, states that a preservative is on the market which con- 

 tains a nitrite in addition to formaldehyde: the nitrite masks 

 the usual reactions but its effect may be destroyed by the 

 addition of a httle urea. 



Boric Acid and Borates. These may be detected by adding 

 a few cubic centimetres of normal alkah to not less than 10 

 cubic centimetres of milk and evaporating to dryness over a 

 small flame. The flame is increased until a black ash results: 

 this is acidified with a few drops of hydrochloric acid. After 

 lixiviation with a few cubic centimetres of hot water, the ash is 

 removed by filtration through paper. A turmeric paper is 

 placed in the filtrate in such a manner that only a portion of it 

 can be wetted, and the liquid evaporated to dryness. A red- 

 dish-brown colouration of the wetted portion, due to the for- 

 mation of rosocyanin, indicates the presence of boron com- 

 pounds. A drop of caustic soda changes the colouration to 

 various shades of green and purple which can be restored to 

 the original colour by the addition of hydrochloric acid. 



A useful routine method for the detection of boron com- 

 pounds consists in heating about 10 c.cms. of milk in a porce- 

 lain dish with a few cubic centimetres of methyl alcohol and a 

 few drops of tincture of turmeric. The heating is conveni- 

 ently carried out in a water bath and the presence of boron 

 compounds is indicated by the formation of a reddish ring 

 roimd the basin. 



The estimation of boron compounds is most conveniently 

 carried out by Thomson's method.^ One or two cubic centi- 

 metres of N-NaOH are added to 100 c.cms. of milk and the 

 whole evaporated to dryness in a platinum dish. The residue 

 is ignited to a black ash, heated with 20 c.cms. of water and 

 concentrated hydrochloric acid added, drop by drop, until 

 frothing ceases. The solution containing the carbonaceous 



