30 On Alkaline Colour Properties. [1822. 



however, so many substances possessing this property, that it 

 must either be limited more exactly than has yet been done, or 

 else given up as a distinguishing property. 



All the soluble salts of iron that I have tried, except the ace- 

 tate, brown turmeric paper. Weak solutions of the green and 

 red muriate seem very alkaline indeed, and even common green 

 vitriol strongly so. They do not, however, produce the same 

 effect on rhubarb paper, but the persalts give it an olive-green 

 tint, whilst the protosalts produce no change at first, but gra- 

 dually give green tints, apparently from becoming persalts. 



If a strong solution of muriate of zinc be boiled on zinc, it 

 gradually oxidizes the metal and dissolves it ; and a concen- 

 trated solution is obtained, which, when diluted, deposits either 

 an oxide or a submuriate of zinc. This strong solution is 

 apparently alkaline to turmeric paper. If it be diluted with 

 about its bulk of water, and filtered, it will still redden turmeric 

 paper, though it proves slightly acid by litmus paper. If 

 further diluted, more precipitate will fall, and the solution will 

 appear alkaline or not, according as the dilution has been small 

 or great. This substance has the same effect on rhubarb paper, 

 and the tint is very like that of a true alkali. 



The acid nitrate of bismuth appears alkaline to turmeric ; if 

 diluted till a little oxide becomes deposited, it is more so : the 

 common solution of chloride of antimony in muriatic acid added 

 to water till a precipitate falls, appears alkaline : permuriate 

 of tin produces a strong change ; protomuriate of tin a very 

 decided reddening; sulphate of tin, slight only. When the 

 acid nitrate of bismuth, and the three salts of tin mentioned, 

 are applied to rhubarb paper, they produce but little effect at 

 first, but if dried by the fire, it becomes quite brown. 



A strong solution of chloride of manganese seems feebly but 

 evidently alkaline to turmeric paper. 



It may be supposed, that with many of these substances the 

 effect is produced principally by the acid present, inasmuch as 

 they were all more or less acid to litmus, and it has been shown 

 that these bodies, especially nitric acid, have this power. But 

 the very slight excess in some of them, as in the salts of iron, 

 zinc, manganese, &c., and the greater effect produced by further 

 dilution, as with bismuth and antimony, show that the whole 

 substance must act ; for if it be considered due to the acid 



