JS6 METHOD OF OBTAINING OXIGEN GAS.

apparatus to the rays of the sun, and very pure oxigen gas willbe liberated.

The emission of oxigen gas is proportioned to the vigour of theplant and the vivacity of the light; the quantity differs in diffe-rent plants and under different conditions. (See page 120.)

Rationale. ..It is an established fact, that plants decomposewater and probably carbonic acid, which serve for their nourish-ment ; they absorb the hidrogen and carbon of these fluids, dis-engaging part of the oxigen in a state of purity. Light howeverfavours this decomposition greatly, it seems to serve for meltingthe oxigen and thus forms it into oxigen gas; in proportion as itbecomes disengaged, the hidrogen becomes fixed in the vegetableand combines partly with the carbon, and partly with the oxigen,to form the oil, &c. of the vegetable.

3. Nitrate of potash is another substance frequently made useof for obtaining oxigen gas, in the following manner:

Take any quantity of this salt, introduce it into a coatedearthen or glass retort, and fit to it a tube, which must beplunged into the pneumatic trough, under the receiver filled withwater. When the apparatus has been properly adjusted, heaftheretort gradually till it becomes red-hot; the oxigen gas will thenbe disengaged rapidly.

The gas obtained in this way is also very pure, especially ifthe last portion be kept separate.

Rationale. ..Nitrate of potash consists of nitric acid andpotash. Nitric acid consists again of oxigen and nitrogen. Onexposing the salt to ignition, a partial decomposition of the acidtakes place; the greatest part of the oxigen of the nitric acidunites to caloric, and appears under the form of oxigen gas. Theother part remains attached to the potash in the state of nitrousacid. The residue in the retort is therefore nitrite of potash, ifthe process has been carefully conducted.

Remark. ..If too much heat be applied, particularly towardsthe end of the process, a total decomposition of the nitric acidtakes place, the oxigen gas in that case will therefore be mingled