1 72 On tJic Relation of Acids and Alkalis to vegetable Colours. 



verted not only to turmeric, but to other vegetable colours, as 

 Syrup of Violets, Tincture of Cabbage, Columbine, &c. 



In the " Transactions of tlie Royal Society of London," 

 Mr. Smithson has ingeniously supposed that the transit from 

 red to blue, exhibited on the rupture of the leaves of the red 

 cabbage, &c. is owing to the escape of carbonic acid gas. This 

 liowever is most certainly not the case. I am induced to 

 ascribe it to the loss of a portion of its latent caloric, for the 

 following reasons : If the vessels be ruptured in a heated at- 

 mosphere, the colour contimies red. If the blue infusion be 

 heated, it becomes red, which is completely fatal to Mr. Smith- 

 son's conclusion. The Tincture of Cabbage will even change 

 to red in a tube hermetically seeded. 



Simply heat blue litmus paper or misized paper tinged with 

 Tincture of Cabbage, and such will become red ; and the or-i- 

 ginal blue colour isoill be restored on dipping the paper into 

 diluted alkali. 



Let paper stained with Tincture of Cabbage, and subse- 

 quently reddened with acetous at id, be exposed to the effects of 

 radiation in an unclouded nocturnal sky, and the blue colour will 

 return. 



I found that a portion of ice well washed with distilled water, 

 turned the Tincture of Red Beet to a permanent dark brown. 



In fact, I have found that heat, in mimerous cases, has super- 

 induced a change of colour similar to that effected by acids, and 

 cold similar to those changes connected with alkaline action. 



These facts clearly prove that we have been completely wrong- 

 in the lines of demarcation we hove drawn around alkalis and 

 acids in their relations to vegetable colours as characteristic of 

 their respective features ; and I cannot doubt that a more 

 subtile and refined chemistry, the result of an extended stage 

 of our beautiful science, will reveal to us many more blots; — 

 blots that the hand of experiment only can deface. 

 With every res}:>ect I have the honour to be. 

 Gentlemen, 

 Your nuich obliged and very obedient humble ser\ant, 



J. Murray. 



Aug. 2, 1 822. 

 I believe (for in truth I very seldom read over what I have 

 written, certainly never take or retain a copy of my conmui- 

 nications) I omitted to note, " on the relation of acids and al- 

 kalis to vegetable colours," that the superacetafe of lead turns 

 the Syrup of Violets greeti, the same change being superin- 

 duced, as in the case of subacetate of lead; — thei'e is therefore 

 no necessity lor ringing changes on that solilaiy string. 



It 



