QUALITIES. _Form_, crystals whose primitive form is the regular tetrahedron, although it assumes a variety of secondary forms. _Colour_, white. _Odour_, none. _Taste_, slightly styptic and metallic; on exposure to the air, the crystals slightly effloresce and become opaque; thrown upon burning coals, they become black and afford metallic antimony. CHEMICAL COMPOSITION. This is involved in much doubt and obscurity; it is stated in the various dispensatories to be a triple salt, consisting of tartaric acid, oxide of antimony,[378] and potass, and which therefore, says Mr. Thomson, on the principles of the reformed nomenclature, ought to be termed a _tartrate of antimony and potass_. The truth of these views, however, is extremely questionable. I am inclined to believe with Gay Lussac, that in the various metalline compounds, of which super-tartrate of potass is an ingredient, this latter substance acts the part of a simple acid; an opinion which receives much support from the great solvent property of cream of tartar, and from the striking fact that it is even capable of dissolving various oxides which are insoluble in tartaric acid, of which the protoxide of antimony is an example. According then to this view, tartar emetic is a salt composed of bi-tartrate (_super-tartrate_) of potass, which acts the part of an acid, and protoxide of antimony: from the experiments of Mr. Phillips, it would appear that 100 parts of the bi-tartrate will dissolve 70 of the protoxide. In this state of doubt it must be admitted that no name can be more appropriate than _Antimonium Tartarizatum_, and the London College have therefore properly disregarded the suggestions which have been offered for changing its name. SOLUBILITY. Much discrepancy of opinion exists upon this subject, owing probably to the variations and incidental impurities to which the salt is liable. Dr. Duncan, who selected very pure specimens for examination, states that it is soluble in three times its weight of water at 212°, and in fifteen at 60°. This solution, when the salt is pure, is perfectly clear and transparent, but if long kept, unless a portion of spirit be added, it undergoes decomposition; a precipitate indeed sometimes takes place very rapidly, but this is generally tartrate of lime, an incidental impurity, derived from the super-tartrate of potass. INCOMPATIBLE SUBSTANCES. _Mineral Acids, Alkalies, and their Carbonates, most of the Metals, Soaps, Hydro-Sulphurets, and many infusions and decoctions of bitter and astringent Vegetables_, e. g. f℥j. of the decoction of yellow bark is capable of completely decomposing ℈j of this salt, and of rendering it inert.[379] Berthollet has accordingly recommended the immediate exhibition of this decoction when an overdose of the salt has been taken; and Orfila has given a very satisfactory case in which this antidote succeeded. Infusion and tincture of galls throw down curdled and inert precipitates of a dirty white colour, inclining to yellow.