pyro graph

[Pref. pyro-, and Gr. grapho = to write, to draw.] An apparatus for engraving on wood or leather by means of a red-hot metallic point. The most improved form of this apparatus consists of a tube six inches in length and about half an inch in diameter, provided at its lower extremity with a screw-cap and a small support. At the other end there is a bent rod, to which the drawing point is fixed by means of a screw. For the formation of the combustible gas and the heating of the rod, sulphuric ether is employed. This liquid, like benzine, is quite inflammable, and care must be taken not to pour it out near a flame. In a closed receptacle it is safe enough. After the flame has been regulated it is po ible to work for two consecutive hours at an expense of a cent for ether. The vapors disengage themselves constantly and feed the small flame, which is barely perceptible. The heat is always uniform, and even on leather a sure and sharp execution of the design is po ible. gun-cotton, which contains about 13 per cent. of The finest and most delicate lines can be drawn, and nitrogen and collodion containing about 111⁄2 per there is no danger of burning holes in the material. cent. The great advantages of the new powder are As the left hand is free, the object to be ornamented its homogeneity of substance and its regularity and completene of combustion. It develops greater initial velocities with smaller pre ure than the old forms of smoke-giving powders. IMG:content-0021.png:[blocks in formation] Chemistry: C6H6O3=C6H3(OH)3. Pyrogallol. An acid, discovered by Scheele, who considered it sublimed gallic acid, and prepared it by heating gallic acid in a stream of carbonic anhydride. It crystallizes in long flattened prisms, soluble in water, slightly soluble in alcohol and ether, melts at 115°, and boils at 210°. Its solutions reduce the salts of gold, silver, and mercury, and give a deep blue color with ferrous salts. It di olves in potash or soda, forming a solution which rapidly absorbs oxygen from the air and turns black. Extensively used in photography as a reducing agent. Its salts, the pyrogallates, are little known. can be turned in any position while the work is in progre .