1821.] Action of Boracic Acid on Turmeric. 27 



may be used. I constructed some angular tubes of long nar- 

 row slips of glass and wood, placing three or four together, so 

 as to form a triangular or square tube, tying them round with 

 packthread, and easily obtained tones from hydrogen by means 

 of them ; and it is evident that variations of the channel, the 

 use of which is to form and direct the current of air, may be 

 made without end. May 11, 1818. 



Boracic Acid, action on Turmeric*. 



IT may be observed, in connexion with the changes of colour 

 produced by acids, that boracic acid reddens turmeric paper in 

 all states of dilution. When a very weak solution is used, it 

 requires a few minutes to produce the effect ; but when pro- 

 duced, it exactly resembles that of alkali. It has been said 

 that strong solutions of alkaline borates, which have been made 

 purposely acid, have become alkaline on being diluted. This 

 has probably arisen from a careless observance of the effect 

 above noticed, and a want of corroboration by the effect on 

 litmus paper of the diluted solution. I find that solutions once 

 made acid redden litmus paper, however diluted ; though at 

 the same time they also redden turmeric paper. Paper co- 

 loured by rhubarb is not affected in this way. 



Boracic Acid^. 



I MENTIONED above 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 (Annales de Chimie, xvi. p. 75), apparently without a 

 knowledge of the previous remark ; and he has shown 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. 



* Quarterly Journal of Science, vi. 152. f Ibid. xi. 403. 



