Chemical Science. 403 



23. Singular Property of Boracic Acid. — I mentioned in the 

 6th vol. of this Journal, p. 152 (1819), the property possessed 

 by boracic acid in all states of dilution, of reddening turmeric 

 paper in the manner of an alkali. Since then the attention of 

 M. Desfosses has been drawn to the action of boracic acid on 

 this colouring matter {Annates de Chimie, xvi. p. 75.), apparently 

 without a knowledge of the previous remark ; and he has shewn 

 that a mixture of boracic, with other acids, reddens turmeric very 

 deeply, and that turmeric, when acted on by this mixture of 

 acids, has its nature altered, for it approaches somewhat to 

 turnsole, and is rendered blue by alkalies. 



There is something so curious in this action of boracic acid, 

 on turmeric, that I am tempted to offer a few more results on 

 the subject. 



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 pro- 

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

 colouring matter are entirely different to what they were before : 

 sulphuric, 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 

 contrary make it blue, gradually passing to shades of purplish 

 blue, yellowish red, Sfc. As long as the acids or alkalies remain 

 on the paper, if not so strong as to destroy the colouring 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 

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

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

 turmeric 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 sun-light 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 alkaline 

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

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

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

 ammonia easily washes out, and the blue tint disappears, and 



