The percentic amounts of carbon and hydrogen contained in organic substances are determined for the most part by a process of combustion, and, taking sugar by way of example, the method may be described as follows: A definite weight is taken and, after admixture with oxide of copper, placed in a little vessel or boat small enough to be pushed into a length of glass combustion tubing. The tube containing the boat is then placed in a socalled combustion rurnace as shown in figure, suitably equipped and connected with, first of all, a dryingtube of previously ascertained weight, and then with socalled potash bulbs charged with a solution of potassium hydroxide of sp. gr. 126, also of previously ascertained weight. This socalled “combustion furnace” is extensively employed for exposing solid substances up to a rod heat to a current of air, oxygen, or other gas, in order to study the. effects produced, by subsequent examination of the gaseous and residual products, and still more often for the analytical determination of the constituents of organic substances. It consists of a great number of Bunsen burners set in a row, and all rising up from a larger gassupply pipe below, with which they are connected. They sometimes terminate in and are surrounded by hollow perfi irated cones or blocks of earthenware, as shown by d in illustration, which has the effect of breaking up the flame and bringing the entire mass to a glowing red heat when in use. The framework is of iron, and so constructed that when the furnace is in use, the heat can be more or less concentrated on the combustiontube by means of earthenware tiles arranged at the. sides, and which can also be placed over the top of the channel in which the combustiontube rests. Reverting now to the analysis of sugar, a current of dried oxygen gas is passed through the combustiontube, while gradually heated to redness in the furnace. This causes the decomposition of the sugar, which consists of carbon, hydrogen, and oxygen, with the result that the carbon is burned off as carbon dioxide and the hydrogen as water. The water is absorbed by the sulphuric acid or calcium chloride contained in the dryingtube and the carbon dioxide is absorbed by the potash m the bulbs and these being severally weighed after the combustion is completed, it is known that the increases in weight of the two appliances are due to these absorbed products, and knowing how much carbon and hydrogen are severally contained in given quantities of carbon dioxide and water, it is easy to calculate the quantities therefrom. These will be found to make up so much of the weight of the sugar, and the other part necessarily consists of oxygen, which is the only other constituent of the sugar, and which it is therefore unnecessary to specifically determine otherwise. To determine the nitrogen content of organic substances the combustion is, in the main, conducted as already described, but a current of carbon dioxide is first of all used to clear out the air from the combustion apparatus, and afterwards to sweep out any remaining nitrogen gas, which is collected by displacement in an inverted tube of mercury standing in a dish of potassium hydrate, and measured, and from this measurement its weight is calculated. Any oxygen that may be admixed with the nitrogen gas is first of all absorbed by introducing an alkaline solution of pyrogallic acid. In other cases, instead of using cupric oxide, fused lead chromate reduced to powder is employed, and there are wellunderstood methods of determiirng the percentages of any other constituents, such as sulphur or phosphorus.
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