HEMATINE is the name given by its discoverer, Chevreul, to a crystalline sub stance, of a pale pink color, and brilliant lustre when viewed in a lens, which he extracted from logwood, the hcentatoxylon, Campechianum of botanists. It is, in fact, the characteristic principle of this dye wood. To proeurelaematine, digest, dur ing a few hours, ground logwood in water heated to a temperature of about 130° F. ; filter the liquor, evaporate it to dryness by a steam bath, and put the ex tract in alcohol of 0.835 for a day. Then filter anew, and after having inspissated the alcohol solution by evaporation, pour it into a little water, evaporate gently again, and then leave it to itself in a cool place. In this way a considerable quan tity of crystals of hematine will he ob tained, which may be readily purified by washing with alcohol and drying.
When subjected to dry distillation in a retort, hematine affords all the usual products of vegetable bodies, along with a little ammonia ,• which proves the pre sence of azote. Boiling water dissolves it abundantly, and assumes an orange red color, which passes into yellow by cooling, but becomes red again with heat. Sulphurous acid destroys the color of solution of hematine. Potash and am monia convert into a dark purple-red tint, the pale solution of hematine ; when these alkalis are added in large quantity, they make the color violet blue, then brown red, and lastly brown-yellow. By this
time, the bematine has become decom posed, and cannot be restored to its pris tine state by neutralizing the alkalies with acids.
The waters of baryte, strontia, and lime exercise an analogous power of decompo sition ; but they eventually precipitate the changed coloring matter.
A red solution of hematine subjected to a current of snlphureted hydrogen be comes yellow ; but it resumes its original hue when the sulphureted hydrogen is removed by a littlepotash.
The protoxyde of lead, the protoxyde of tin, the hydrate of peroxyde of iron, the hydrate of oxydes of copper and nickel, oxyde of bismuth, combine with hematine, and color it blue with more or less of a violet east.
Hematine precipitates glue from its so lution in reddish flocks. This substance has not hitherto been employed in its pure state; but as it constitutes the ac tive principle of logwood, it enters as an ingredient into all the colors made with that dye-stuff.
These colors are principally violet and black. Chevreul has proposed hematine as an excellent test of acidity.