ORGANIC ANALYSIS. 69J) 



is represented by the excess of its weight over the sum of the 

 weights of the carbon, hydrogen and nitrogen found. I shall 

 merely sketch the outline of this fundamental and highly im- 

 portant process, referring for the minute instructions necessary 

 for its exact execution to Professor Liebig's valuable tract on 

 Organic Analysis.* 



The nitrate of copper, decomposed by a red heat in an 

 earthenware crucible, gives a fine light oxide, very suitable for 

 the combustion process, and of which a considerable quantity 

 must be provided. It is a property of this oxide to be reduced 

 with extreme facility at a red heat, by carbon or hydrogen, and 

 at the same time to resist an intense temperature, when heated 

 apart from combustible matter, without losing a particle of 

 oxygen. The substance to be analysed, or burnt with oxide of 

 copper, we shall suppose to be sugar. 



The tube for combustion is of the most difficultly fusible glass, 

 free from lead ; no variety answers better for it than the 

 white Bohemian glass. It is generally about 0.4 inch in inter- 

 nal diameter, and 14 or 15 inches long, drawn out, bent and 

 FIG. 85. sealed at one end, 



as represented (Fi- 



some measure of the quantity of oxide of copper to mix with 

 the substance to be analysed, the tube is to be filled to 

 three fourths of its length with pure oxide of copper, out 

 of a crucible in which it has just been ignited, and while 

 it is yet warm. From 5 to 7 grains of dry loaf sugar in 

 fine powder are first rubbed in a porcelain mortar with a little 

 oxide, with which it is intimately mixed, and by degrees the 

 whole oxide of copper is added, which was measured in the 

 tube. Having first introduced pure oxide of copper, so as to 

 fill about half an inch at the closed end of the tube, the mixture 

 from the mortar is then introduced, followed by a portion of 

 oxide employed to rinse out the mortar, and the last covered 

 by pure oxide, so as to fill up the tube to within one inch of 



* Translated by Dr. W. Gregory, and forming Part I of Griffin's Scientific Mis- 

 cellany. Tegg, London. 



z z 2 



