CHEMICAL APPARATUS. 81 



continued use of nitrous oxyde, however, must be very inju- 

 rious, since animals confined in this gas soon die. 



To procure Oxygen from Fig. 532. 



Black Oxyde of Manga- 

 nese. (Fig. 532.) Put 

 into an iron retort half a 

 pound of the black oxyde 

 of manganese in powder. 

 Place it in the fire, and 



when approaching a red \ 



heat oxygen gas will begin 

 to pass out at the open end, as may be known by the in- 

 creased flame of a candle held to it. When this is the case, 

 fasten a collapsed bladder to the open end of the barrel, so 

 as to be air-tight, when the gas will pass into it, and may 

 be preserved for use. This quantity of oxyde should make 

 about two gallons and a half of gas ; it is not perfectly 

 pure, but sufficiently so for ordinary experiments. Instead 

 of the bladder, convey the liberated gas either to a gas- 

 holder, or to glass-receivers, placed upon the shelf of the 

 pneumatic trough for its reception. 



To procure Oxygen from Chlorate of Potash. A more 

 convenient mode of preparing oxygen gas, is to put in a 

 glass retort, or flask, having a bent tube, a quantity of chlo- 

 rate of potash, mixing with it about one-fourth part of black 

 oxyde of manganese, and apply the heat of a spirit lamp ; 

 when the gas will be freely disengaged, and may be col- 

 lected beneath a bell glass upon a pneumatic trough, or 

 received directly into a flexible gas bag. 



The Gasometer. (Fig. 533, next page.) The gasometer 

 is usually made of japanned tin or copper. It consists of an 

 outer circular vessel, to the sides of which are fastened two 

 round tubes, running upright, and about double the height 

 of the vessel below. Across the top of these tubes is fixed 

 a similar one that is square, which has a hole in the centre, 

 and is furnished with two small pulleys near this hole, one on 



