f H 1 brightens it very much. As the fyrup of violets is apt to ferment in hot countries, it is better to take a piece of the inlpifiated fuccus heliotrtjpii f/. g. tumefolf or fome of the abovementioned linen rags tinged with radifhes, and to employ them, On a voyage or journey ; becaufe it is very eafy to make a tincture of turnefol, or lacmufs^ with water. 32. It muft however be oblerved, that a volatile fulphureous acid deftroys the colours, and that a folution of alum will fometimes pro duce the fame effects which acids will, in changing blue and purple made of vegetables into red. EXPERIMENT X. 33. If you have an alkaline fait, which you know to be fuch (for inftance, fait of tartar, or fpirit of hartfhorn), and you want to examine fome fluid, in order to afcertain whether it be an acid, put fome folution of one of the alkaline falts into it, and it will caufe an efferveicence* if the fluid be an acid ; and if you continue ter put gradually fo much of an alkaline folution to it, till the ebullition, heat, and vapours fub- fide, you have faturated or neutralized the' liquors \ or it may be faid you have brought the fluids to the point of faturation ; and after the fuperfluous water is evaporated,'‘the neutra lized fait will fhoot into regular figures, or cryjlallize, and then become a neutral or falind fait. EXPERIMENT XI. 34. If the fyrup or tincElure of violets, or cyanus, or the tincture of litmufs, or the purple-co loured rags, mentioned in Experiment IX. turn