172 SCIOPTICON MANUAL. 



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 PREPARATION OF OX YUEN GAS. 



MATERIALS. Theoretically, one pound of chlorate of 

 potash should yield 37 gallons, or 5 cubic feet of 

 oxygen gas; or enough to fill the ordinary 30 by 40 

 inch rubber bag. In common practice, however, it takes 

 20 ounces to get 5 feet, or a quarter of a pound to a 

 cubic foot. 



To facilitate the decomposition at a lower tempera- 

 ture, and to moderate the flow of gas, we mix with the 

 20 ounces of chlorate of potash about 5 ounces of black 

 oxide of manganese. 



To be assured that this black powder is no part char- 

 coal, black lead, sulphide of antimony, or any thing else 

 that will make with the chlorate of potash an explosive 

 mixture, we may mix and heat a sample of a new sup- 

 ply on a scrap of sheet-iron, or in an iron spoon, over a 

 lamp. If it simply melts and dries away, leaving a dark 

 gray residuum it is safe ; if it flashes up, leaving a whitish 

 residuum it is unsafe. 



For habitual use, it is convenient to keep this oxygen 

 mixture in stock. Put into a box, say 20 pounds of 

 pure chlorate of potash, broken, so as to pass readily 

 into the retort. Add to these white, broken crystals, 5 

 pounds of black oxide of manganese, and stir the two 

 well together into a dark gray mass. A pint cup is con- 

 venient as the measure of a " charge/' as it holds besides 

 the manganese about a pound of the chlorate. 



THE APPARATUS. A gas stove, a (Fig. 46), where 

 we may have it, is, perhaps, the most convenient heat- 

 ing apparatus. An alcohol lamp, as commonly recom- 

 mended, is too slow, or else with larger wicks it is in 

 danger of explosion. A kitchen stove is better, either 

 in the kettle's place with a brisk fire, or else upon the 

 live coals. 



