. Elements of chemistry ... ed of carbon 6,and oxygen 16=22. Now, since there was only 15 grainsof the wood, we infer that 1 proportion of the oxygen wasderived from the wood, and 1 proportion from the oxide ofcopper. The substance to be analysed must first be reduced topowder, if capable, if not into small pieces, and mixed withabout 100 times its wTeight of oxide of copper, then the mix-ture is to be dried in the vacuum of an air pump, whereinis also a .small vessel of sulphuric acid. The substance foranalysis is first heated to about 212°, or higher if it will bearit, and in this state set
. Elements of chemistry ... ed of carbon 6,and oxygen 16=22. Now, since there was only 15 grainsof the wood, we infer that 1 proportion of the oxygen wasderived from the wood, and 1 proportion from the oxide ofcopper. The substance to be analysed must first be reduced topowder, if capable, if not into small pieces, and mixed withabout 100 times its wTeight of oxide of copper, then the mix-ture is to be dried in the vacuum of an air pump, whereinis also a .small vessel of sulphuric acid. The substance foranalysis is first heated to about 212°, or higher if it will bearit, and in this state set under the receiver, before containingthe acid, and then the air exhausted. The acid by its affin-ity to water, abstracts all the moisture still retained by thesubstance in the dish. The mixture Fig. 81. to be analysed being thus pre- tL$\ (^j pared, it is intro-duced into thetube of greenglass, a, Fig. 81,which is open at the large end, and drawn out into a finepoint at the other, to which is attached the small glass globe. 330 VEGETATION. c, communicating with the pipe d, which contains chloride ofcalcium. From the tube d, there passes a crooked tube,leading under the bell-glass f. which stands in the mercurybath g. The orifice of the tube a, being closed by a pieceof clay or otherwise, the tube is heated very gradually byburning charcoal, the screen b: according to the directions ofProf. Mitscherlich, being necessary for the purpose of pre-venting the heat from spreading too rapidly, lest the glassshould become fused. By means of the heat, the carbon and hydrogen of thesubstance to be analysed, unite with the oxygen given outby the oxide of copper, so that a complete combustion goeson within the tube, and water and carbonic acid are com-posed. The water collects in the globe c, and if any vaporpasses, it is absorbed by the chloride of potash in the tube part of the apparatus being carefully weighed bothbefore and after the process, the excess of weight must bedue to t
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