Traite Elcmentairc dcs RcacHfs. 335 



a property of great consequence in the purification of beet-root 

 sugar. 



To distinguish a very small quantity of essential oil in a distilled 

 water, a few drops of solution of muriate of gold are employed. 

 The metal is reduced by the oil, and falls down in a violet powder. 

 Or. coloured tests for acidity and alkalinity, MM. Payen and 

 Chcvallier give us less definite mformation than we had expected. 

 The alcoholic infusion of wild mallow petals, yields by evapora- 

 tion, a colouring matter, which dissolved in water, is sensibly 

 greened by a water containing j^tJoiTTT ^^ hydrate of potash, or 

 TooW^ of hydrate of soda. Lime water, with 10 additional 

 waters, is the limit of dilution at which the mallow paper can b.e 

 affected ; but with 25 waters, the mallow infusion is still greened. 

 Water boiled on calcined magnesia and then filtered, is capable of 

 affecting the same test. 



Litmus paper, according to Bergman, is sensible to ^^Vr of free 

 sulphuric acid in water ; but not to a less proportion. The tincture 

 or litmus is, however, much more sensible. When a drop of 

 water impregnated with carbonic acid is applied to strongly dyed 

 litmus paper, no change ensues, because the alkali of the litmus is 

 adequate to the saturation of the minute quantity of that acid in a 

 drop of the liquid; but the same water when poured into a weak in- 

 fusion of litmus, reddens it perceptibly. In MM. Payen and Ceval- 

 lier's paper on the wood of St, Lucie, it is stated that water contain- 

 ing -gTj'y^ of sulphuric acid just reddens paper stained violet with 

 an infusion of the fruit of that wood ; but the infusion itself is 

 sensible to acid diluted to -^jy^-^s- Litmus paper is said to be 

 sensible to xioItt^' ^^^ '^^ tincture is a still more delicate test. 

 Paper, stained red with infusion of Brazil wood, is an excellent 

 re-agent for distinguishing several acids from one another. — Sec 

 the extract of M. Bonsdorft''s Memoir in this Journal XIV. 226. 

 Paper stained yellow with turmeric is browned by water contain- 

 ing TT^Jpj- of dry carbonate of soda; but it must be some time 

 immersed in the liquid. This test is, however, of little use in 

 determing alkalinity, since Mr. Faraday has shewn that it is liable 

 to be browned by strong acids, as also by the boracic, by the 

 green sulphate and muriate of iron, sub-muriate of zinc, super- 

 nitrate of bismuth, diluted chloride of antimony, of a strong 

 solution of muriate of manganese, muriate, sulphate, acetate, ancl 

 nitrate of uranium, and muriate of zirconia. Sec this Journal 

 X1IL315, XIV. 234. Rhubarb colour has similar fallacies. Mr. 

 South shewed long ago, that subacetate of lead reddens turmeric. 



Brazil wood is a pretty delicate test of alkalis ; but it is blued 

 by waters containing earthy carbonates, and sulphate of lime. 

 Water holding in solution -iYuhrtT) ^^ <^''y carbonate of soda, aO'ccts 

 Brazil wood paper. Kirwan says, however, that it is not aflected 

 by water impregnated with ^^-^^ of selenite. Reddened litmus 

 paper is blued by water which contains -jVtj ^^ ^'•"Y carbonate of 

 soda, according to Bergman. Infusion of red cabbage or of violets, 

 Vol. XV. Z 



