28 Boracic Acid. [1821. 



Turmeric paper dipped into a solution of pure boracic acid 

 very speedily receives a slight tint of brownish-red, which, when 

 the paper is dry, is very marked, and resembles that produced 

 by a weak alkali. In this state the properties of the colouring 

 matter are entirely different to what they were before : sul- 

 phuric, nitric, muriatic, and phosphoric acids, even when very 

 dilute, produce a bright red colour on this paper, and a strong 

 solution of oxalic acid also reddens it. Alkalies, on the con- 

 trary, make it blue, gradually passing to shades of purplish- 

 blue, yellowish-red, &c. As long as the acids or alkalies 

 remain on the paper, if not so strong as to destroy the colour- 

 ing matter, the new colour remains, but a slight washing removes 

 them, and then the boracic acid tint returns, and the paper has 

 its first peculiar properties. When altered by muriatic acid or 

 ammonia, the mere volatilization restores the paper to its first 

 state ; with the ammonia the restoration is very ready and per- 

 fect ; with the acid it is longer and not so complete. If the 

 paper reddened by boracic acid be heated, the yellow of the tur- 

 meric is almost restored, and then it takes from acids a weaker 

 red tinge, and from alkalies a more purplish colour than before. 



Turmeric, thus altered by boracic acid, is readily restored to 

 its original state by washing ; altered turmeric paper when put 

 in water for two or three hours resumes its original properties, 

 and acts, as at first, in testing the alkalies. 



When the altered paper is placed in sunlight a few days, 

 the colour is soon destroyed as with turmeric alone, and then 

 neither acid nor alkali will affect it. 



When turmeric paper is dipped into neutral or slightly alka- 

 line borate of ammonia, it soon becomes of the red tint produced 

 by boracic acid, and is in every respect as if altered by bo- 

 racic acid alone ; when this paper is made blue by ammonia, 

 the ammonia easily washes out and the blue tint disappears, 

 and afterwards the boracic acid or borates will wash out and 

 leave the paper as at first. 



Borax itself at first reddens turmeric paper because of the 

 excess of -alkali, but as the colouring matter becomes altered by 

 the presence of the boracic acid, the tint becomes of a dirty 

 bluish colour, and then the paper is changed by acids or alka- 

 lies, just as if it had been altered by boracic acid. 



Hence it is probable that the neutral borates have the same 



