316 Faraday on Alkaline Properties. 



At Vol. VI. p. 152, and XI. p. 403, I have shewn the effect 

 of boracic acid, in reddening turmeric paper. Mr. South, I 

 believe, first shewed, that the sub-acetate of lead reddened tur- 

 meric, and this has been considered sufficient evidence by many, 

 that the oxide of lead merited, in some degree, the name of ao 

 alkali. I find on trial, 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 pro- 

 perty. 



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

 acetate, 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 per salts give it an olive- 

 green tint, whilst the proto salts produce no change at first, 

 but gradually give green tints, apparently fr6m becoming per 

 salts. 



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 sub-muriate of zinc. This strong solution is ap- 

 parently alkaline to tumeric paper. If it be diluted with about 

 its bulk of water, and filtered, it will still redden tumeric 

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

 ther 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 tumeric ; 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 : — per muriate 

 of tin produces a strong change ; proto-muriate of tin a very 

 decided redding ; 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 become quite brown. 



